C++ :

#include<iostream>
#include<algorithm>
using namespace std;
const int N = 100000;
int a[N],b[N];

void addfact(int n,int a[],int b[]){
	fill(a,a+N,0);
	fill(b,b+N,0);
	a[0]=a[1]=b[0]=1;
	for (int i=1; i<=n; i++)
	{
		for (int j=1; j<=a[0]; j++) a[j]*=i;
		for (int j=1; j<=a[0]; j++)
		{
			a[j+1]+=a[j]/10;
			a[j]%=10;
		}
		while (a[a[0]+1])
		{
			a[0]++;
			a[a[0]+1]=a[a[0]]/10;
			a[a[0]]%=10;
		}
		b[0]=a[0]>b[0]?a[0]:b[0];
		for (int j=1; j<=b[0]; j++)
		{
			b[j]+=a[j];
			b[j+1]+=b[j]/10;
			b[j]%=10;
		}
		while (b[b[0]+1])
		{
			b[0]++;
			b[b[0]+1]=b[b[0]]/10;
			b[b[0]]%=10;
		}
	}
}

void output(int a[]){
	for (int i=a[0]; i>=1; i--) cout<<a[i];
	cout<<endl;
}

int main(){
	int n;
	cin>>n;
	addfact(n,a,b);
	output(b);
	return 0;
}