#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("factorial.in");
ofstream fout("factorial.out");
int p;
int main()
{
    fin>>p;
    int st=1,dr=1<<20;
    int sol=-1;
    if (p==1) fout<<1;
    else
    {
        while (st<=dr)
        {
            int mij=(st+dr)/2;
            int z=0;
            for (int i=5;i<=mij;i*=5)
                z+=mij/i;
            if (z==p) {sol=mij;dr=mij-1;}
            else if (z<p) st=mij+1;
            else if (z>p) dr=mij-1;
        }
        fout<<sol;
    }

    return 0;
}