#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,i;
    for(i=5;i<=h;i=i*5)
        rez=rez+h/i;
    return rez;
}

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

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