#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");

long long catidezero (long long P)
{
    long long i=5,contor=0;
    while (i<=P)
    {
        contor+=(P/i);
        i*=5;
    }
    return contor;
}
int main()
{
    long long P,cP,st,dr,mij,fi;
    fin >> P;
    if (P==0)
    {
        cP=1;
        fout << cP;
    }
    else
    {
        st=1;
        dr=500000000;
        while (st<dr)
        {
            mij=(st+dr)/2;
            fi=catidezero(mij);
            if (fi<P)
            {
                st=mij+1;
            }
            if (fi>P)
            {
                dr=mij-1;
            }
            else if (fi==P)
            {
                while (catidezero(mij)==P)
                {
                    --mij;
                }
                ++mij;
                fout << mij;
                return 0;
            }
        }
        cP=-1;
        fout << cP;
    }
}