#include<bits/stdc++.h>
using namespace std;
int main(){
	int i=1,h=0,n,j,b;
	cin>>n;
	for(i=1;i<=n;i++){
		j=i;
		if(i%5==0){
			while(j>0){
				b=j%10;
				j=j/10;
				if(b==5){
					h++;
					break;
				}
			}
		}
	}
	   cout<<h<<endl;
} 
/**************************************************************
	Problem: 1057
	User: fuyijun
	Language: C++
	Result: Accepted
	Time:20 ms
	Memory:2072 kb
****************************************************************/