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

}

/**************************************************************
	Problem: 1057
	User: 15159808820
	Language: C++
	Result: Accepted
	Time:18 ms
	Memory:2072 kb
****************************************************************/