HDU 1396 Counting Triangles

#include <iostream>
#include <cstdio>

using namespace std;

long long int CountTriangle[1000010];

int main()
{
int i,j,n;

long long int sum;

CountTriangle[1] = 1;
CountTriangle[0] = 0;

for(i = 2;i <= 500; ++i)
{
for(n = i/2,sum = 2*i-1,j = 2;j <= n; ++j)
{
sum += i-j+1 + i-j-j+1;
}
for(;j <= i; j++)
sum += i-j+1;
CountTriangle[i] = sum + CountTriangle[i-1];
}

while(cin>>n)
{
if(n <= 0)
cout<<0<<endl;
else
cout<<CountTriangle
<<endl;
}

return 0;
}