rt，（虽然一开始忘记特判WA了第二个点

#include<bits/stdc++.h>
#define ull unsigned long long
#define ll long long
#define ft int
ft qread(){ft f=1, a=0;char ch;ch=getchar();for(; !isdigit(ch); ch=getchar()){if(ch=='-'){f=-1;}}for(; isdigit(ch); ch=getchar()){a=a*10+ch-'0';}return a*f;}
void write(ft x){if(x<0){putchar('-');x=-x;}if(x<10){putchar(x+'0');return ;}write(x/10);putchar(x%10+'0');}
using namespace std;
const int INF=0x3f3f3f3f, N=1e5+5;
stack<int> s;
int n, ans;
int main(){
	n=qread();
	if((n!=3 && n<5) || n==7){
		puts("-1");
		return 0;
	}
	ans=n/5;
	if(n%5==0)
		write(ans);
	else if(n%5==1)
		write(ans+1);
	else if(n%5==2)
		write(ans+2);
	else if(n%5==3)
		write(ans+1);
	else
		write(ans+2);
	return 0;
}