#include <fstream>
#include <algorithm>
#include <iostream>
using namespace std;
int main(){
	int p,n;
	ifstream f1("fact.in");
	ofstream f2("fact.out");
	f1>>p;
	int n2,n5;
	n2=0;n5=0;
	for(n=1;min(n2,n5)!=p;n++){
	 int aux=n;
     while(aux%2==0){
      n2++;aux/=2;
	 }
	 aux=n;
     while(aux%5==0){
      n5++;aux/=5;
	 }
    }
 f2<<n-1;
 }