#include<bits/stdc++.h>
using namespace std;
int main()
{
	int N,i,a=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)
	a++;
	}
	cout<<a;
	return 0;
}

/**************************************************************
	Problem: 1057
	User: ccf
	Language: C++
	Result: Accepted
	Time:15 ms
	Memory:2072 kb
****************************************************************/