#include<bits/stdc++.h>
using namespace std;

int n;
vector<int> ans;

vector<int> add(vector<int> a,vector<int> b){
	vector<int> res;
	res.resize(114514);
	int x = 0;
	for(int i = 0;i < max(a.size(),b.size());i++){
		res[i] = a[i] + b[i] + x;
		x = res[i] / 10;
		res[i] %= 10;
	}
	return res;
}
vector<int> cf(vector<int> a,int b){
	vector<int> res;
	res.resize(114514);
	int x = 0;
	for(int i = 0;i < a.size();i++){
		res[i] = a[i] * b + x;
		x = res[i] / 10;
		res[i] %= 10;
	}
	return res;
}
vector<int> fact(int x){
	vector<int> res;
	res[0] = 1;
	for(int i = 1;i <= x;i++){
		res = cf(res,i);
	}
	return res;
}

int main(){
	cin>>n;
	for(int i = 1;i <= n;i++){
		ans = add(ans,fact(i));
	}
	bool flag = false;
	for(int i = ans.size() - 1;i >= 0;i--){
		if(ans[i] == 0 && !flag) continue;
		else{
			cout<<ans[i];
			flag = true;
		}
	}
	return 0;
}

编译器：TDM-GCC 4.9.2 64-bit Debug