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

ifstream f;
ofstream g;

long int n,k,p;

main()
{

f.open("fact.in");
g.open("fact.out");

f>>p;
n=0;
k=0;
while(k<p){
           n+=5;
           if((n/5)%5==0)k+=2;
           else k++;
           }

if(n==0)g<<"1";
else g<<n;
g.close();
}