#include <fstream>
#include <cmath>
using namespace std;
int main ()
{
    ifstream fin ("fact.in");
    ofstream fout ("fact.out");
    int p,n,k,a;
    n=1;
    fin>>p;
    k=1;
    a=1;
    while(p!=0)
    {
        n++;
        if(n==pow(5.0,(double)k)) {p--; k++;}
        if(n==pow(10.0,(double)a)) {p--; a++;}
    }
    fout<<n;
    fin.close();
    fout.close();
}