#include <iostream>
#include <fstream>
#include <climits>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int n,sol=-1;
long long p,ex,mij,ex5,ls=1,ld=INT_MAX-2;
int main()
{
    f>>p;
    while(ls<=ld)
    {
       mij=(ls+ld)/2;
       ex=5;
       ex5=0;
       while(ex<=mij)
           {
               ex5+=mij/ex;
               ex*=5;

            }
        if(ex5>=p)
           {
               ld=mij-1;
                sol=mij;
           }
        else ls=mij+1;
    }
    if(sol==-1)
        g<<-1;
    else
        g<<sol;

    return 0;
}