#include <iostream>
#include <fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int p,low=1,high=100000000;
long long mid;
int functie(int val)
{
    int rez=0;
    for(int i=5; i<=val; i*=5)
        rez=rez+val/i;

    return rez;
}
int main()
{
    f>>p;
    while(low<high)
    {
        mid=low+(high-low)/2;
        if(functie(mid)>=p)
            high=mid;
        else low=mid+1;
    }
    mid=(low+high)/2;
    if(functie(mid)==p)
        g<<mid;
    else g<<-1;

    return 0;
}