求1到n的阶乘之和的 c++程序 急急急急急急

#include <iostream>

using namespace std;

long sum = 1;
long countall = 1;

int main(int argc, char *argv[])
{
cout << "Please input max N : ";
int iNum;
cin >> iNum;
cout << "User input : " << iNum << endl;

for(int i=2; i<=iNum; i++)
{
sum = sum*i;
countall += sum;
}
cout << "Total value is : " << countall << endl;

return 0;
}