#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: wangchenyu
	Language: C++
	Result: Accepted
	Time:16 ms
	Memory:2072 kb
****************************************************************/