#include <stdio.h>
int fact(int n)
{
	int i, s = 1;
	for (i = 1; i <= n; i++)
		s = s * i;
	printf("%d", s);
	return 0; 
}
int nr_cifre(int n)
{
	int nr = 0;
	while(n){
	n /= 10;
	nr++;
	}
	printf("%d", nr);
	return 0;
}
int main()
{
	int p,i,n = 1;
	freopen("fact.in", "r", stdin);
	freopen("fact.out", "w", stdout);

	scanf("%d",&p);
	
	while(n){
	if(nr_cifre(fact(n))==p){
		printf("%d", n);
		break;
	}
	n++;
	}
	
	return 0;
}