C++ :

#include<iostream>
#include<algorithm>
using namespace std;
const int N = 6000;
int a[N];

void fact(int n){
	fill(a,a+N,0);
	a[0]=a[1]=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;
		}
	}
}

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

int main(){
	int n;
	cin>>n;
	fact(n);
	output(a);
	return 0;
}

Pascal :

var
i,k,j,n:longint;
s:array[1..6000] of integer;
f:boolean;
begin
  k:=6000;
  f:=false;
 s[k]:=1;
 readln(n);
 for j:=1 to n do
 begin
 for i:=k downto 1 do
   s[i]:=s[i]*j;

 for i:=k downto 1 do
   if s[i]>=10 then
   begin
   s[i-1]:=s[i-1]+s[i] div 10;
   s[i]:=s[i] mod 10;
   end;
   end;
  for i:=1 to k do
   if (s[i]>0) or (f) then begin write(s[i]);f:=true;end;
   end.