神奇的题面。

#include<bits/stdc++.h>
#define int long long
#define INF 0x3f3f3f
using namespace std;
int n,m;
signed main(){
	cin>>n>>m;
	cout<<(2*n+m-1)*m/2;
	return 0;
}

不给样例？

#include<iostream>
using namespace std;
signed main(){
	int n,m;
	cin>>n>>m;
	cout<<(2*n+m-1)*m/2;
}