    def find(i, ss, step):
        for j in range(step, len(ss)):
            #print(i, j, ss[j])
            if i == ss[j]:
                a = j
                return a, step
        return -1
     
     
    s = input().strip()
    #print(s)
    t = input().strip()
    #print(t)
    ss = s * 100
    #print(ss)
    step = 0
    for i in t:
        a = find(i, ss, step)
        if a == -1:
            print(-1)
            break
        else:
            #print(a)
            step = a[0] + 1
            #print(step)
    if a != -1:
        print(step)