#include <bits/stdc++.h>


#define ll long long

using namespace std;

int main() {
    ios_base::sync_with_stdio(0);cin.tie(0); cout.tie(0);
    ll n, m, t; cin >> n >> m >> t;
    ll l = 0, r = min(n, m)+1;
    while (r - l > 1){
        ll o = (r+l)/2;
        if (m - 2 * o < 0 || n - 2 * o < 0) {
            r = o;
        }
        else if(n*m - (n-2*o)*(m-2*o) > t){
            r = o;
        }
        else l = o;
    }
    cout << l;
    return 0;
}