#include<iostream>
#include<string.h>
using namespace std;
const int INF=0x3f3f3f3f;
const int N=2e5+10;
long long n,x,a[N],len; 
int main(){
	cin>>n;
	a[++len]=1;
	for(int i=1;i<=n;i++){
		for(int j=1;j<=len;j++){
			a[j]=a[j]*i+x;
			x=a[j]/10;
			a[j]%=10;
		} 
		while(x){
			a[++len]=x%10;
			x/=10;
		}
	}
	for(int i=len;i>=1;i--){
		cout<<a[i];
	}
}

#include <iostream>
#include <vector>
using namespace std;

// 计算阶乘的函数，返回存储阶乘结果的数组，低位在前
vector<int> factorial(int n) {
    vector<int> result(1, 1);  // 初始化为1，低位在前，方便计算
    for (int i = 2; i <= n; ++i) {
        int carry = 0;
        for (size_t j = 0; j < result.size(); ++j) {
            int product = result[j] * i + carry;
            result[j] = product % 10;
            carry = product / 10;
        }
        while (carry > 0) {
            result.push_back(carry % 10);
            carry /= 10;
        }
    }
    return result;
}

int main() {
    int n;
    cin >> n;
    if (n == 0 || n == 1) {
        cout << 1 << endl;
        return 0;
    }
    vector<int> res = factorial(n);
    // 从高位到低位输出结果
    for (auto it = res.rbegin(); it != res.rend(); ++it) {
        cout << *it;
    }
    cout << endl;
    return 0;
}

100%AC不AC我倒立洗头

#include<iostream>
#include<cstring>
#include<cmath>
#include<iomanip>
#include<queue>
#include<algorithm>
#include<vector>
#include<stack>
using namespace std;
#define LL long long
const int N=1e5+10;
using namespace std;
int n , ans[N] , len , x;
int main()
{
	
	cin>>n;
	ans[++len] = 1;
	for(int i = 2; i <= n; i++)
	{
		for(int j = 1; j <= len; j++)
		{
			ans[j] = ans[j] * i + x;
			x = ans[j] / 10;
			ans[j] %= 10;
		}
		
		while( x )
		{
			ans[++len] = x % 10;
			x /= 10;
		}
	}
	for(int i = len; i >= 1; i --)
		cout << ans[i];
	return 0;
}

#include<iostream>
#include<string.h>
using namespace std;
const int INF=0x3f3f3f3f;
const int N=2e5+10;
long long n,x,a[N],len; 
int main(){
	cin>>n;
	a[++len]=1;
	for(int i=1;i<=n;i++){
		for(int j=1;j<=len;j++){
			a[j]=a[j]*i+x;
			x=a[j]/10;
			a[j]%=10;
		} 
		while(x){
			a[++len]=x%10;
			x/=10;
		}
	}
	for(int i=len;i>=1;i--){
		cout<<a[i];
	}
}

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

const int N=1e6+10;
long long a,b,c,d,e,f,g;
double x,y,z;
int n[N];
 
int main(){
	cin>>a;
	n[++b]=1;
	for(int i=1;i<=a;i++){
		for(int j=1;j<=b;j++){
			n[j]=n[j]*i+c;
			c=n[j]/10;
			n[j]%=10;
		}
		while(c){
			n[++b]=c%10;
			c/=10;
		}
	}
	for(int i=b;i>=1;i--)cout<<n[i];
	return 0;
}