#include<bits/stdc++.h>
using namespace std;
int main(){
    int N,i,s;
    s=0; 
    cin>>N;
    for (i=5;i<=N;i+=5){
    if (i%10==5||i%100/10==5||i%1000/100==5||i%10000/1000==5)
    s++;                
    }
    cout<<s;    
    return 0;
}

/**************************************************************
	Problem: 1057
	User: chenmingyu
	Language: C++
	Result: Accepted
	Time:15 ms
	Memory:2072 kb
****************************************************************/