Help me in solving NUMREC problem

My issue

My code

#include <iostream>
using namespace std;

int main() {
	// your code goes here
	int k;
	    int n,m;
	return 0;

Problem Link: CodeChef: Practical coding for everyone


Its a simple maths pnc question we use to do in class 11th
the total number of rectangle possible and (((n+1)*(n))/2 )*(((m+1)*(m))/2);
now u have to subtract the rectangle   having (n,m) cell which will be nothing but n * m;
so just subtract the n*m  from the total number of rectangles.

It’s showing partial_correct.