#include <bits/stdc++.h>
using namespace std;
int main(){
	int N,i,s=0;
	cin>>N;
	for(i=5;i<=N;i+=5) {
	if(i%10==5||i%100/10==5||i%1000/100==5||i%10000/1000==5) s=s+1;}
	cout<<s;
	return 0;
	}

/**************************************************************
	Problem: 1057
	User: ljl2
	Language: C++
	Result: Accepted
	Time:13 ms
	Memory:2072 kb
****************************************************************/