#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: wngjinming
	Language: C++
	Result: Accepted
	Time:20 ms
	Memory:2072 kb
****************************************************************/