#include <iostream>
#include <fstream>
#include <algorithm>

using namespace std;

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

int nrZero(int val) {
    int nr = 0, p = 5;
    while (p <= val) {
        nr += val / p;
        p *= 5;
    }
    return nr;
}

int cautareBinara(int val) {
    if (val == 1) {
        return 5;
    }
    int stg = 0, dr = 5 * val;
    while (stg < dr) {
        int mij = (stg + dr) / 2;
        if (nrZero(mij) == val) {
            dr = mij;
        }
        else {
            stg = mij + 1;
        }
    }
    return stg;
}

int main() {
    int p;
    fin >> p;
    fout << cautareBinara(p);
    fin.close();
    fout.close();
    return 0;
}