#2337 Coada2

#include <bits/stdc++.h>
using namespace std;
long long x, y, z;
int main()
{
    ifstream f("coada2.in");
 ofstream g("coada2.out");
    f >> x >> y >> z;

    if(x >= y || x >= z) g << -1;
                   else  g << y + z - x;
    return 0;
}