#include<bits/stdc++.h> 
using namespace std;
int main(){
	int g,N,i,j,h=0;
	cin>>N;
	for(i=1;i<=N;i++){
		j=i;
		if(j%5==0){
		  while(j>0){
			g=j%10;
			j=j/10;
			if(g==5){
				h++;
				break;	
			}
	    }   
	}
} 
	    cout<<h;
		return 0;
	}
/**************************************************************
	Problem: 1057
	User: zhangchenhao
	Language: C++
	Result: Accepted
	Time:15 ms
	Memory:2072 kb
****************************************************************/