下面程序的输出为（ ）。
#include <iostream>using namespace std;int main() { int N = 15, cnt = 0; for (int x = 1; x + x + x <= N; x++) for (int y = x; x + y + y <= N; y++) for (int z = y; x + y + z <= N; z++) cnt++; cout << cnt << endl; return 0;}