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

ifstream in("fact.in");
ofstream out("fact.out");
long long n,p,z;

void citire()
{
    in >> p;
}

int nrz(int m)
{
 int nr=0,div=5;
 while(m/div!=0){
  nr= nr+ m/div;
  div=div*5;
 }
 return nr;
}




int main()
{
    citire();
    long long st = 1,dr = 1000000000,mij,poz=-1;
    while(st<=dr)
    {
        mij = (st + dr)/2;
        z = nrz(mij);
        if(z>=p)
        {
            if(z==p)
                poz = mij;
            dr = mij -1;
        }
        else
            st = mij + 1;
    }
    out << poz;

    return 0;
}