放心，保准AC

点个关注吧

#include<bits/stdc++.h>
using namespace std;
int Shift1(int n){//意思是“！”
    int sum = 1;
    for(int i = 1; i <= n; i++){
        sum *= i;
    }return sum;
}int main(){
    int a, num = 0;
    cin >> a;
    vector<int>sum = {};
    for(int i = 1; i <= a; i++){//放入数组sum
        sum.push_back(Shift1(i));
    }for(int i = 0; i < a; i++){//把数组sum的每一项加到num
        num += sum[i];
    }cout << num;
}