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

}
/**************************************************************
	Problem: 1057
	User: houshanglin
	Language: C++
	Result: Accepted
	Time:19 ms
	Memory:2072 kb
****************************************************************/