#include<iostream>
#include <fstream>

using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");
long long nr,n,m,nr1;
 int main()
{   in>>nr;
    n=nr*4;

    while(nr1<nr)
    {   nr1=0;
        m=n;

    while(m!=0)
    {  m/=5;
        nr1+=m;}
    n++;
    }

  if(nr1!=nr) out<<-1;
    else if(nr==0) out<<1;
        else out<<n-1;


return 0;
}