C++ :

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<iomanip>
#include<cstdlib>
#include<cmath>
#include<cstring>
#include<string>
#include<cctype>
using namespace std;
int m;
long long a[100001];
int main(){
	memset(a,0,sizeof(a));
	a[1]=1;a[0]=1;
	int i,j;
	scanf("%d",&m);
	for(i=1;i<=m;i++){
		for(j=1;j<=a[0];j++){
			a[j]*=i;
		}
		for(j=1;j<=a[0];j++){
			if(a[j]>9) {
				a[j+1]+=a[j]/10;
				a[j]%=10;
			}
		}
		while(a[a[0]+1]>0) {
			a[0]++;
			if(a[a[0]]>9){
				a[a[0]+1]+=a[a[0]]/10;
				a[a[0]]%=10;
			}
		}
	}
	for(i=a[0];i>0;i--) printf("%ld",a[i]);
	cout<<endl;
	return 0;
}

Pascal :

var
   n,i:longint;
   s:int64;
begin
 readln(n);
 s:=1;
 for i:=1 to n do s:=s*i;
 writeln(s);
end.