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

int p,i,n2,n5,aux;

int main()
{ifstream g("fact.in");
g>>p;
i=1;
while((n2<p)||(n5<p))
{aux=i;
while(aux%2==0)
     {n2++;
      aux/=2;}
while(aux%5==0)
     {n5++;
      aux/=5;}
i++;}
ofstream t("fact.out");
if(i-1==0)
	t<<1;
else
    t<<i-1;
t.close();
g.close();
return 0;}