#include <iostream>
#include <fstream>
#include <cmath>
#include <limits>
using namespace std;
 
int verificare(int nr)
{
    int count = 0;
    int putere_cinci = 5;
    while(nr/putere_cinci > 0)
    {
        count = count + nr/putere_cinci;
        putere_cinci = putere_cinci * 5;
    }
    return count;
}
 
int main()
{
    ifstream f("fact.in");
    ofstream g("fact.out");
 
    int stanga, dreapta, mijloc;
    int p;
    f>>p;
 
    stanga = 1;
    dreapta = p*5;
    while(stanga <= dreapta)
    {
        mijloc = (stanga + dreapta)/2;
        if(verificare(mijloc) < p) stanga = mijloc + 1;
        else dreapta = mijloc - 1;
    }
    if(verificare(stanga) == p) g<<stanga;
    else g<<-1;
 
    cout<<endl;
    return 0;
}