#include <iostream>
#include <fstream>

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

long p,n;

int nrdezero (int x)
{
    int p=5,nr=0;
    while (p<=x)
    {
        nr+=x/p;
        p*=5;
    }
    return nr;
}

void bin_search()
{
    long long left=1,right=1200000000,mid,nr=-1;
    while (left<=right)
    {
        mid=(left+right)/2;
        int aux=nrdezero(mid);
        if (aux<p)
            left=mid+1;
        if(aux>p)
            right=mid-1;
        if (aux==p)
        {
            nr=mid;right=mid-1;
        }
    }
    g<<nr<<"\n";
}

int main()
{
    f>>p;
    bin_search();
    f.close();
    g.close();
    return 0;
}