Project Euler 28

#include <iostream>

using namespace std;
int sum(int L)
{
    int n = L*L;
    int sum = n,
        res = L-1,
        i;
    while(n>=1 && res >=0)
    {
        for(i = 1; i<=4 && res>1 ; i++)
        {
            n = n-res;
            sum += n;
        }
        res-=2;
    }
    return sum;
}
int main()
{
    cout << sum(1001)<< endl;
    return 0;
}