#include <bits/stdc++.h>
using namespace std;
int main() {
int a,b,c,n;
int left = n-a-b+c;
if(left<=0||(a<c&&b<c)||(a!=0&&b<c)||(b!=0&&a<c))
cout<<-1;
else
cout<<left;
return 0;
}
I2luY2x1ZGUgPGJpdHMvc3RkYysrLmg+CnVzaW5nIG5hbWVzcGFjZSBzdGQ7CgppbnQgbWFpbigpIHsKCWludCBhLGIsYyxuOwoJaW50IGxlZnQgPSBuLWEtYitjOwoJaWYobGVmdDw9MHx8KGE8YyYmYjxjKXx8KGEhPTAmJmI8Yyl8fChiIT0wJiZhPGMpKQoJY291dDw8LTE7CgllbHNlCgljb3V0PDxsZWZ0OwoJcmV0dXJuIDA7Cn0=