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 * 500
#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)
