小凯的疑惑

找规律

#include <cstdio>
#include <iostream>
#include <algorithm>
#include <cstring>
#include <cmath>
#define int long long 
using namespace std;
int a,b,ans=0;

signed	main()
{
	scanf("%lld %lld",&a,&b);
	if(a>b)	swap(a,b);
	int c;
	printf("%lld",(a-1)*b-a);
}