#include<bits/stdc++.h>
using namespace std;
int main(){
	int n,i,g,h=0,j;
	cin>>n;
	for(i=1;i<=n;i++){
		j=i;
		while(j!=0){
			g=j%10;
			j=j/10;
			if(i%5==0&&g==5){
				h++;
				break;
			}	
		}
	}
	cout<<h;
}


/**************************************************************
	Problem: 1057
	User: fandaohan
	Language: C++
	Result: Accepted
	Time:33 ms
	Memory:2072 kb
****************************************************************/