#include <fstream>
#include <iostream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int putere(int n){
	int k=0;
	k=0;
 while(n%5==0){n=n/5; k++;}
	return k;
	
}
int main(){
	int n,i,OK,nr,cinci;
	f>>n;
	OK=0;
	nr=1;
	while(OK==0)
	{//cout<<nr;
		cinci=0;
		for(i=5;i<=nr;i++)
			{cinci+=putere(i);
			}//for
	if(cinci>=n)
		OK=1;
	nr++;
	}//while
g<<nr-1;
	/*cout<<putere(30);
	cout<<endl;
	*/
	
}