#include <bits/stdc++.h>
using namespace std; //Writing this at the start so as not define namespace everytime
int countFaults(int x, int y, int z) {
int ans = -1;
if (abs(x-y) > z) return ans;
return max(x,y) + (z-abs(x-y))/2;
}
int main()
{
cout << countFaults(4, 4, 4) << endl;
cout << countFaults(2, 5, 4) << endl;
cout << countFaults(5, 2, 4) << endl;
cout << countFaults(2, 5, 8) << endl;
return 0;
}
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