// 最左侧冗余覆盖子串
func HW2023028() {
// 测试用例
// let s1 = "ab", s2 = "aabcd", k = 1
// let s1 = "abc", s2 = "dfs", k = 2
// 开始代码
let s1 = String(readLine()!)
let s2 = String(readLine()!)
let k = Int(readLine()!)!
let strLen = s1.count + k
let len = s2.count - strLen + 1
var res = -1
for i in 0..<(len>0 ? len : 0) { // 滑动窗口
let temp = String(s2.dropFirst(i).prefix(strLen))
// 判断s1是否是temp的子串，如果是则返回当前下标
if Set(Array(s1)).isSubset(of: Set(Array(temp))) {
res = i
break
}
}
print(res)
}
