s = input()
t = input()

#contest
#son
wrap = 0
index = -1
for  i in t:
    index = s.find(i,index+1)
    if index != -1:
        continue
    wrap +=1
    index = s.find(i)
    if index ==  -1:
        print(-1)
        exit()
print(len(s)*wrap+index+1)