VS上能过，但是洛谷全RE

#include<iostream>
#include<cstring>
#include<algorithm>
#define MAXN 5000
using namespace std;
struct bigint {
    int len, a[MAXN];
    bigint(int x=0) {              //构造函数，默认时为零
        memset(a, 0, sizeof(a));
        for (len = 1; x; len++)
            a[len] += x % 10, x /= 10;
        len--;
    }
    int &operator[](int i) {
        return a[i];
    }
    void flatten(int L) {       //处理进位
        len = L;
        for (int i = 1; i < len; i++)
            a[len + 1] += a[len] / 10, a[len] %= 10;
        for (; !a[len];)
            len--;
    }
    void print() {
        for (int i = max(1,len); i >= 1; i--)
            cout << a[i];
    }
};
bigint &operator +(bigint a, bigint b) {    //高精加高精
    bigint c;
    int len = max(a.len, b.len);
    for (int i = 1; i <= len; i++)
        c[i] = a[i] + b[i];
    c.flatten(len+1);
    return c;
}

bigint& operator*(bigint a, int b) {        //高精乘低精
    bigint c;
    int len=a.len;
    for (int i = 1; i <= len; i++)
        c[i] = a[i] *b;
    c.flatten(len + 10);                    //int 最多10位（long long 最多19位）
    return c;
}
int main() {
    bigint ans(0), fac(1);                  //ans是阶乘之和，fac是阶乘
    int n;
    cin >> n;
    for (int i = 1; i <= n; i++){
        fac = fac * i;
        ans = ans+fac;
    }
    ans.print();
    return 0;
}