'''
并查集实现, 拓展版本，可以用回调把数据转成内部key, 然后内部用线性表来实现
'''

class MergeSetExt:
    def __init__(self, max_key_val = 0, trans_key_func=None):
        if trans_key_func is not None and max_key_val > 0:
            # 如果能够提供转换key的回调，并查集内部用线性表存储
            self.trans_key_callback = trans_key_func
            self.m = [-1 for _ in range(max_key_val+1)]
            self.__root2cluster_size = [0 for _ in range(max_key_val+1)]
        else:
            # 如果不能提供转换key的回调，并查集内部用hash表存储
            self.trans_key_callback = None
            self.m = {}
            self.__root2cluster_size = {}
        self.__root_cnt = 0

    def getRoot(self, node):
        buf = []
        root = self.trans_key_callback(node) if self.trans_key_callback else node
        while self.m[root] != root:
            buf.append(root)
            root = self.m[root]
        for key in buf:
            self.m[key] = root

        return root

    def merge(self, a, b):
        orig_a, orig_b = a, b
        if self.trans_key_callback:
            a, b = self.trans_key_callback(a), self.trans_key_callback(b)

        for node in [a, b]:
            if (self.trans_key_callback is None and node not in self.m) or (self.trans_key_callback is not None and self.m[node] == -1):
                self.m[node] = node
                self.__root2cluster_size[node] = 1
                self.__root_cnt += 1

        root1 = self.getRoot(orig_a)
        root2 = self.getRoot(orig_b)
        if root1 != root2:
            self.m[root1] = root2

            self.__root2cluster_size[root2] += self.__root2cluster_size[root1]
            if self.trans_key_callback:
                self.__root2cluster_size[root1] = 0
            else:
                self.__root2cluster_size.pop(root1)
            self.__root_cnt -= 1

    # 根据根节点的数值获取其所在的簇的大小
    def getClusterSize(self, root):
        return self.__root2cluster_size[root]

    def isInSameSet(self, a, b):
        if a == b:
            return True

        orig_a, orig_b = a, b
        if self.trans_key_callback:
            a, b = self.trans_key_callback(a), self.trans_key_callback(b)

            for node in [a, b]:
                if self.m[node] == -1:
                    return False
        else:
            for node in [orig_a, orig_b]:
                if node not in self.m:
                    return False

        return self.getRoot(orig_a) == self.getRoot(orig_b)

    def getRootNum(self):
        return self.__root_cnt

    def getClusters(self):
        rec = {}
        if self.trans_key_callback is None:
            for node in self.m:
                root = self.getRoot(node)
                if root not in rec:
                    rec[root] = []
                rec[root].append(node)
        else:
            for node in range(len(self.m)):
                if self.m[node] == -1:
                    continue

                root = self.getRoot(node)
                if root not in rec:
                    rec[root] = []
                rec[root].append(node)

        return [nodes for nodes in rec.values()]



m, n = map(int, input().split())

# 克鲁斯卡尔算法求解最小生成树输入为边列表，每条边表示为(起点，终点，权重)
# 返回最小生成树权重总和，以及最小生成树边列表, 生成不了最小生成树返回None
def getMinSpanTreeKruscal(init_edges):
    merge_set = MergeSetExt(m*n+1, lambda x : (x[0]-1)*n + x[1])

    sum = 0
    cnt = 0
    for a1, b1, a2, b2 in init_edges:
        if not merge_set.isInSameSet((a1, b1), (a2, b2)):
            merge_set.merge((a1, b1), (a2, b2))
            cnt += 1

    for i in range(1, m+1):
        for j in range(1, n+1):
            if i+1 <= m:
                a1, b1, a2, b2, w = i, j, i+1, j, 1

                if merge_set.isInSameSet((a1, b1), (a2, b2)):
                    continue

                merge_set.merge((a1, b1), (a2, b2))
                sum += w
                cnt += 1

                if cnt == m*n - 1:
                    return sum

    for i in range(1, m+1):
        for j in range(1, n+1):
            if j+1 <= n:
                a1, b1, a2, b2, w = i, j, i, j+1, 2

                if merge_set.isInSameSet((a1, b1), (a2, b2)):
                    continue

                merge_set.merge((a1, b1), (a2, b2))
                sum += w
                cnt += 1

                if cnt == m*n - 1:
                    return sum
    return sum


init_edges = []

while True:
    try:
        i1, j1, i2, j2 = map(int, input().split())
        init_edges.append((i1, j1, i2, j2))
    except:
        break

print(getMinSpanTreeKruscal(init_edges))