#include <fstream>
using namespace std;

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

int main(){
    long long p, i, n = 0, nr, nrz;
    fin >> p;
    if (p == 0){
        fout << 1;
        return 0;
    }
    i = 5;
    while (p){
        nr = i;
        nrz = 0;
        while (nr%5 == 0){
            nr /= 5;
            nrz++;
        }
        n += 5;
        p -= nrz;
        i += 5;
    }
    fout << n;
    fin.close();
    fout.close();
    return 0;
}