#include<bits/stdc++.h>
using namespace std;
int main(){
	int n,a,b,c=1,d=0;
	cin>>n;
	while(n>=c){
		a=c;
		while(a>0){
			b=a%10;
			a=a/10;
			if(b==5){
				if(c%5==0){
					d++;
					break;
				}
			}
		}
		c++;
	}
    cout<<d;	
}
	    

	    
	
 

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