View Code of Problem 18

#include<bits/stdc++.h>
using namespace std;

int main() {

	int n;
	while(cin>>n){
		if(n<3){
			cout<<0<<endl;
		}else{
			int num=0;
			num++;
			n-=2;
			for(int i=1;i<n;i++){
				num+=i;
			}
			cout<<num<<endl;
		}
	}


	return 0;
}