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

/**************************************************************
	Problem: 1057
	User: lzk
	Language: C++
	Result: Accepted
	Time:17 ms
	Memory:2072 kb
****************************************************************/