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

/**************************************************************
	Problem: 1057
	User: linzihang
	Language: C++
	Result: Accepted
	Time:18 ms
	Memory:2072 kb
****************************************************************/