#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/10%10==5||i/100%10==5||i/1000%10==5)
		s++; 
		
	}
	cout<<s;
	

	return 0;
}

/**************************************************************
	Problem: 1057
	User: 21A
	Language: C++
	Result: Accepted
	Time:15 ms
	Memory:2072 kb
****************************************************************/