#include <bits/stdc++.h>

using namespace std;

int main() {

    long long x,y,
              ans = 0;
    unsigned long long d;

    cin >> x >> y >> d;

    vector<vector<bool> > grid(d+1,vector<bool>(d+1,false));

    for(int i = 0;i <=d;i++){
        int dx = i,
            dy = d-i;
        grid[dx][dy] = true;
    }

    for(int i = 0;i <= x;i++){
        for(int j = 0;j <= y;j++){
            if(grid[i][j]) ans++;
        }
    }

    cout << ans << endl;

    return 0;
}