#include <iostream>
#include <fstream>

using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");

int nzero(int p)
{
    int fact5 = 5, ans5 = 0;
    while(fact5 <= p)
    {
        ans5 += p / fact5;
        fact5 *= 5;
    }

    return ans5;
}


int main()
{
    int p;

    fin >> p;

    int st = 1, dr = 5 * 1e8, sol = -1;
    while(st <= dr)
    {
        int mij = (st + dr) / 2, cntzero = nzero(mij);

        if(cntzero >= p)
        {
            dr = mij - 1;
            if(cntzero == p)
                sol = mij;
        }
        else
            st = mij + 1;
    }
    fout << sol;

    return 0;
}