Codeforces Round #409 (rated, Div. 2, based on VK Cup 2017 Round 2) B. Valued Keys

只要y的每个字母都小于等于x的就直接把y输出，否则输出-1

#include<bits/stdc++.h>using namespace std;string s1,s2;int main(){    cin>>s1>>s2;    for(int i=0;i<s1.length();i++)if(s2[i]>s1[i])return cout<<-1,0;    cout<<s2;    return 0;}