#include<fstream>
#include<iostream>
#include<conio.h>
using namespace std;
int p;
void main()
{int k=0,zero=1,numar=1,i=1,fact;

 ifstream f("factorial.in");
 ofstream g("factorial.out");
 f>>p;
 while(k!=p){zero=zero*10;
			 k++;
			}
 while(numar%zero!=0){numar=numar*i;
					 i++;
					 if(numar%zero==0)fact=i;
					 }
 fact--;
 g<<fact;
 f.close();
 g.close();
 
}