#include <bits/stdc++.h>
using namespace std;

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

long long n, st, dr, mij, nr, x;

long long Zero(long long n)
{
    long long s = 0, x = 5;
    while (x <= n)
    {
        s += n / x;
        x *= 5;
    }
    return s;
}

int main()
{
    fin >> n;
    st = 1; dr = 1LL * 5 * (n + 1);
    nr = -1;
    while (st <= dr)
    {
        mij = (st + dr) / 2;
        x = Zero(mij);
        if (x < n) st = mij + 1;
        else if (x > n) dr = mij - 1;
        else
        {
            nr = mij;
            dr = mij - 1;
        }
    }
    fout << nr << "\n";
    return 0;
}