80分代码：

#include <bits/stdc++.h>
using namespace std;
int main(){
	long long x,y,n;
	cin>>x>>y>>n;
	long long shi=0,yi=0;
	long long s1=0,s2=0,sum=0;
	long long x1,y1;
	x1=x-1;
	y1=y-1;
	shi=n/10;
	yi=n%10;
	s1=shi*y1;
	s2=yi*x1;
	sum=s1+s2;
	cout<<sum<<endl;
	return 0;
}