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


/**************************************************************
	Problem: 1057
	User: cx001
	Language: C++
	Result: Accepted
	Time:14 ms
	Memory:2072 kb
****************************************************************/