请问为什么这样写也是2AC，2WA？

#include<iostream>
#include<iomanip>
#include<string>
#include<cmath>
using namespace std;
int main(){
    int n;
    long double sum = 0;
    cin >> n;
    long double currentFactorial = 1;
    for(int i = 1; i <= n; ++i) {
        currentFactorial *= i;
        sum += currentFactorial;
    }
    cout << fixed << setprecision(0) << sum << endl;
    return 0;
}