'''
01分数规划，SPFA判断是否有负环，需要一些玄学剪枝
二分枚举可能的平均值mid, 边权修改为mid - w, 验证
图中是否存在负环
'''


from collections import deque

class SPFA:

    # start_node 为起始点，edges是边的三元组(节点1， 节点2， 边权重) is_directed表示是否是有向图
    # 包含节点为1, 2, 3, 4, ..... max_node_num
    def __init__(self, start_node, edges, is_directed, max_node_num):
        self.edges = edges[::]
        self.start_node = start_node
        self.is_directed = is_directed
        self.max_node_num = max_node_num

    # 获取最短路径长度的列表[(节点1，长度1), (节点2, 长度2) .....]
    def getMinPathLen(self):
        return self.getMinInfo()

    def getMinInfo(self):
        link = {}
        dis = [0x7fffffff] * (self.max_node_num+1)
        dis[self.start_node] = 0

        for a, b, w in self.edges:
            if not self.is_directed:
                # 无向图检查是否有负边
                if w < 0:
                    return None

                if a not in link:
                    link[a] = []
                if b not in link:
                    link[b] = []

                link[a].append((b, w))
                link[b].append((a, w))

            else:
                if a not in link:
                    link[a] = []
                link[a].append((b, w))


        updated_nodes = deque()
        updated_nodes.append(self.start_node)
        in_que = [0] * (self.max_node_num + 1)
        in_que[self.start_node] = 1

        # 进行V次迭代，第V次检查是否是无解情况
        iter_times = 0
        update_cnt = 0

        while iter_times < self.max_node_num:
            update_flag = False

            # 利用上一轮迭代距离变小的点进行松弛操作
            node_num = len(updated_nodes)
            for _ in range(node_num):
                a = updated_nodes.popleft()
                in_que[a] = 0
                if a not in link:
                    continue

                for b, w in link[a]:
                    new_dis = 0x7fffffff if dis[a] == 0x7fffffff else dis[a] + w
                    if new_dis < dis[b]:
                        update_cnt += 1
                        if update_cnt >= self.max_node_num * 5:     # 玄学剪枝
                            return None

                        dis[b] = new_dis
                        update_flag = True

                        if in_que[b] == 0:
                            in_que[b] = 1
                            updated_nodes.append(b)

            iter_times += 1

            if iter_times == self.max_node_num:
                if update_flag:
                    return None

            if not update_flag:
                break

        return [[node, dis[node]] for node in range(1, self.max_node_num+1)]



while True:
    n = int(input())
    if n == 0:
        break

    all_nodes = set()
    e = {}

    for i in range(n):
        s = input()
        a, b = s[:2], s[-2:]
        all_nodes.add(a)
        all_nodes.add(b)
        if (a, b) not in e:
            e[(a, b)] = len(s)
        else:
            e[(a, b)] = max(e[(a, b)], len(s))

    str2idx = {}
    for i, val in enumerate(all_nodes):
        str2idx[val] = i+1

    l, r = 0, 1000
    ans = None
    while abs(r-l) > 1e-3:
        mid = l + (r-l) / 2
        #print(f'mid = {mid}')

        edges = []
        for (a, b), w in e.items():
            a, b = str2idx[a], str2idx[b]
            edges.append((a, b, mid-w))

        for i in range(1, len(all_nodes)+1):
            edges.append((len(all_nodes)+1, i, 0))

        algo = SPFA(len(all_nodes)+1, edges, is_directed=True, max_node_num=len(all_nodes)+1)
        if algo.getMinPathLen() is None:
            ans = mid
            l = mid
        else:
            r = mid

    print('{:.2f}'.format(ans) if ans is not None else 'No solution')