代码如下：

#include <iostream>
#include <algorithm>
#include <cstring>
using namespace std;
struct bi{
	public:
	int num[1000], len = 0;
	bi(string i = "0"){
		memset(num, 0, sizeof(num));
		for(int j = i.length() - 1; j >= 0; j--){
			num[i.length() - j] = i[j] - '0';
			len++;
		}
	}
	int leng(){
		return len;
	}
	void print(){
		for(int i = len; i >= 1; i--){
			cout << num[i];
		}
	}
	bi operator +(bi tee){
		int x = 0;
		bi t;
		int tlen = 0;
		for(int i = 1; i <= max(this->leng(), tee.leng()); i++){
			t.num[i] += x;
			t.num[i] += this->num[i] + tee.num[i];
			x = t.num[i] / 10;
			t.num[i] %= 10;
			tlen++;
		}
		if(x > 0){
			tlen++;
			t.num[tlen] = x;
		}
		t.len = tlen;
		return t;
	}
	bi operator *(int tee){
		int x = 0;
		bi t;
		int tlen = 0;
		for(int i = 1; i <= this->leng(); i++){
			t.num[i] += this->num[i] * tee;
			t.num[i] += x;
			x = t.num[i] / 10;
			t.num[i] %= 10;
			tlen++;
		}
		if(x > 0){
			tlen++;
			t.num[tlen] = x;
		}
		t.len = tlen;
		return t;
	}
};
int main(){
	int n;
	cin >> n;
	bi ans, cur("1");
	for(int i = 1; i <= n; i++){
		cur = (cur * i);
		ans = (ans + cur);
	}
	ans.print();
	cout << endl;
	return 0;
}