AC日记——Valued Keys codeforces 801B

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>

using namespace std;

int len;

char s1[205],s2[205],ans[205];

int main()
{
cin>>s1+1;
cin>>s2+1;
len=strlen(s1+1);
for(int i=1;i<=len;i++)
{
if(s1[i]>=s2[i])
{
ans[i]=s2[i];
}
else
{
printf("-1");
return 0;
}
}
cout<<ans+1;
return 0;
}