#include <iostream>
#include <algorithm>
#include <queue>
#include <string>
using namespace std;

int main(){
    int n;cin>>n;
    
    int ans=0;
    for(int i=10;i<=min(100,n);i++){
        int a=i/10;
        int b=i%10;
        if((a+b)%3==0){
            ans++;
        }
    }
    if(n<=100){
        cout<<ans<<endl;
        return 0;
    }
    queue<string> q;
    q.push("3");
    q.push("6");
    q.push("9");

    while(q.size()){
        string s=q.front();q.pop();
        long long tmp=stoll(s);
        if(100<=tmp&&tmp<=n){
            ans++;
        }
        if(tmp>n){
            continue;
        }
        s+="0";
        q.push(s);
        s.pop_back();
        s+="3";
        q.push(s);
        s.pop_back();
        s+="6";
        q.push(s);
        s.pop_back();
        s+="9";
        q.push(s);
        s.pop_back();
    }

    cout<<ans<<endl;

    return 0;
}