#include <iostream>
using namespace std;
typedef long long ll;

int main()
{
    ll a, b, s;
    cin >> a >> b >> s;
    ll ans = 0;
    for (ll d = 1; d <= a; d++)
    {
        ll e = max(0ll, b - s / d);
        ans += (a + 1 - d) * (b * (b + 1) / 2 - e * (e + 1) / 2);
    }
    cout << ans << endl;
}