#include<fstream>
using namespace std;
ifstream fin("factorial.in");
ofstream fout("factorial.out");
int i, p, v[6], y;
int main() {
    fin >> p;
    i = 1;
    while ((v[2] < p) or (v[5] < p)) {
        y = i;
        if (y % 5 == 0) {
            while (y % 5 == 0) {
                y = y / 5;
                v[5]++;
            }
        }
        if (y % 2 == 0) {
            while (y % 2 == 0) {
                y = y / 2;
                v[2]++;
            }
        }
        i++;
    }
    if (p == 1)
        fout << 0;
    else
        fout << i - 1;
}