def KMP(main_str,sub_str,next_locs):
    main_len = len(main_str)
    sub_len = len(sub_str)
    i, j = 0, 0
    result = -1
    while i < main_len:
        if main_str[i] == sub_str[j]:
            if j >= sub_len - 1:
                result = i - sub_len + 1
                break
            i += 1
            j += 1
        elif next_locs[j] == -1:
            i += 1
            j = 0
        else:
            j = next_locs[j]
    return result


def next_loc(sub_str):
    res = []
    sub_len = len(sub_str)
    for i in range(sub_len):
        if i == 0:
            # sub_str的第一位字符的next()值为 -1
            res.append(-1)
        else:
            k = res[i-1]
            if sub_str[i-1] == sub_str[k]:
                res.append(k+1)
            else:
                # 迭代查找
                while 1:
                    if k == -1:
                        res.append(0)
                        break
                    if sub_str[i-1] == sub_str[res[k]]:
                        res.append(res[k]+1)
                        break
                    k = res[k]
    for i in range(sub_len):
        # 对next()进行改进
        if res[i] != -1 and sub_str[i] == sub_str[res[i]]:
            res[i] = res[res[i]]
            pass
    return res                   

def getResult():
    s = input() # 子串
    l = input() # 

    if set(s) not in set(l):
        return  -1
    next_locs = next_loc(s)
    loc = KMP(l,s,next_locs)
    print(loc)

print(getResult())