#include <algorithm>
#include <iostream>
using namespace std;

int main() {
	long x, y, d;
	cin >> x >> y >> d;
	if (min(x, d) - max(d - y, 0L) >= 0 && min(y, d) - max(d - x, 0L) >= 0) cout << (min(x, d) - max(d - y, 0L)) * ((min(y, d) - max(d - x, 0L))) + 1;
	else cout << 0;
	// cout << (max(min(y, d) - max(d - x, 0L), 0L)) * (max(min(x, d) - max(d - y, 0L), 0L));
}