import java.io.*;
import java.util.*;
public class Main {
public static void main(String[] args) throws IOException{
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
StringTokenizer st = new StringTokenizer(br.readLine());
int N = Integer.parseInt(st.nextToken());
int answer = 0;
while (true) {
if (N % 5 == 0) {
answer += N / 5;
break;
} else {
N -= 3;
answer++;
}
if (N < 0) {
answer = -1;
break;
}
}
System.out.println(answer);
}
}