#include<iostream>
#include<fstream>
using namespace std;

#define n2 (n/2)
#define n5 (n/5)

int main()
{int i=1,p,ct=0;long long n=1;
ifstream fin("fact.in");
fin>>p;
fin.close();

do
{
if((i%2==0)||(i%5==0)) 
{
	if(n2>n5+1) 
		do{n=n2;}while(n2!=n5+1);
	n=n*i;
}
if(n%10==0) {n=n/10;ct++;}
i++;
}while(ct!=p);

i--;
ofstream fout("fact.out");
fout<<i;
fout.close();
return 0;
}