#include <iostream>
#include <fstream>
#include <cmath>

using namespace std;

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

long long int N, P;

int Calcul_Nr_Fact()
{
    int k = 1, nr_fact = 5;
    while(k!=P)
    {
        k = 1;
        nr_fact++;
        for(int i = 5; nr_fact/i >= 1; i *= 5)
            k+= floor(nr_fact/i);
    }
    return nr_fact-1;
}

int main()
{
    fin>>P;
    cout<<Calcul_Nr_Fact();
    return 0;
}