#include <fstream>
#include <iostream>
#include <vector>
using namespace std;

int n, poz = -1;

void read() {
    ifstream f("fact.in");
    f >> n;
    f.close();
}

int verifica(int x) {
    int i, zeros = 0;
    for (i = 244140625; i >= 5; i /= 5) 
        zeros += x / i;
    return zeros;
}

void solve() {
    int st, dr, mij;
    st = 1, dr = 500000000;
    while (st <= dr) {
        mij = (st + dr) / 2;
        if (verifica(mij) >= n) {
            poz = mij;
            dr = mij - 1;
        }
        else st = mij + 1;
    }
}

void output() {
    ofstream g("fact.out");
    g << poz;
    g.close();
}

int main() {
    read();
    solve();
    output();
    return 0;
}