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

ifstream f("fact.in");
ofstream g("fact.out");

long long p;

long long fact(int h)
{
    long long rez=0;
    for(long long i=5;i<=h;i*=5)rez+=h/i;
    return rez;
}

int main()
{
    f>>p;
    long long st=1, dr=p*5, c=0;

    while(st<=dr)
    {
        c=(st+dr)/2;
        if(fact(c)<p)st=c+1;
        else dr=c-1;
    }
    if(fact(st)==p)g<<st;
    else g<<"-1";
    return 0;
}