#include<bits/stdc++.h>
using namespace std;
int main(){
    int n,i,g,h=0,j;
    cin>>n;
    for(i=1;i<=n;i++){
        j=i;
        while(j!=0){
            g=j%10;
            j=j/10;
            if(i%5==0&&g==5){
                h++;
                break;
            }   
        }
    }
    cout<<h;
}
/**************************************************************
	Problem: 1057
	User: huanghengyi
	Language: C
	Result: Compile Error
****************************************************************/