#include<bits/stdc++.h>
using namespace std;
int main(){
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	freopen("road.in","r",stdin);
	freopen("road.out","w",stdout);
	int n,m,p;
	cin>>n>>m>>p;
	cout<<n*m-p-1;
	return 0;
}
