zoj 1629 Counting Triangles

#include<iostream>#include<stdlib.h>using namespace std;int up( int n ){    return (n*(n+1)*(2*n+1)+3*n*(n+1))/12;}int down( int n ){    int sum = 0;    while ( n > 1 ) {        sum += n*(n-1)/2;        n   -= 2;    }    return sum;}int main(){    int n;    while ( cin >> n )         cout << up( n )+down( n ) << endl;    return 0;}