#include <fstream>

using namespace std;

int nr_zero(int n)
{
    int k = 0, f = 5;
    while(n / f != 0)
    {
        k = k + n / f;
        f = f * 5;
    }
    return k;
}

int main()
{
    int p, n;
    ifstream fin("fact.in");
    fin >> p;
    fin.close();
    n = 1;
    while(nr_zero(n) < p)
        n++;
    ofstream fout("fact.out");
    fout << n;
    fout.close();
    return 0;
}