#include <fstream>

using namespace std;

int P, i, nr, res, st, mid ,end;

int main()
{
    ifstream f("fact.in");
    ofstream g("fact.out");

    f >> P;

    end = P * 5;
    if(P == 1)
        st = end + 1, res = 1;
    while(st <= end)
    {
        mid = (st + end) / 2;
        nr = 0;
        for(i = 5; i <= mid; i *= 5)
            nr += mid / i;
        if(nr >= P)
            end = mid - 1, res = mid;
        else st = mid + 1;
    }

    g << res << '\n';

    f.close();
    g.close();

    return 0;
}