#include <fstream>
using namespace std;

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

long long P;
long long zerouri(long long N)
{
    long long rez = 0;
    long long p = 5;
    while (p <= N)
    {
        rez += N / p;
        p *= 5;
    }
    return rez;
}

int main()
{
    fin >> P;

    long long st = 1, dr = 5LL * P, ans = -1;

    while (st <= dr)
    {
        long long mid = (st + dr) / 2;
        long long z = zerouri(mid);

        if (z >= P)
        {
            ans = mid;
            dr = mid - 1;
        }
        else if (z < P)
            st = mid + 1;
    }

    fout << ans;

    return 0;
}