#include <iostream>
#include <fstream>

#include <cmath>
using namespace std;

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

#define lol long long

int get_zeros(int n){
    int k = 0;

    int put = 0;
    while(n>=pow(5, put)){
        put++;
    }
    put -=2;
    return n/5 + put;
}

int main() {
    lol p;
    fin >> p;


    int n = 0;

    int a = get_zeros(n);
    while(a != p){
        a=get_zeros(n);
        n+=5;
    }
    fout << n-5;
}