#include <iostream>
#include <algorithm>
using namespace std;
using ll = long long;

int main(){
    int a, b, s; cin >> a >> b >> s;

    ll ans = 0;
    for(int h = 1; h <= b; h++){
        int w = min(a, s/h);
        ans += 1LL*(b-h+1)*(1LL*a*(a+1)/2-1LL*(a-w)*(a-w+1)/2);
    }
    cout << ans << endl;
    return 0;
}