#include <stdio.h>


int main()
{
	int p,n = 1;
	freopen("fact.in", "r", stdin);
	freopen("fact.out", "w", stdout);

	scanf("%d",&p);
	
	while(n){
	for (i = 1; i <= n; ++i)
		f = f * i;

	while(f){
	f = f/10;
	nr++;
	}
	if(nr == p){
			 printf("%d", n);
			 break;
        } 
	
	n++;
	}
	
	return 0;
}