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

/**************************************************************
	Problem: 1057
	User: LYY001
	Language: C++
	Result: Accepted
	Time:13 ms
	Memory:2072 kb
****************************************************************/