#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); i++)
using namespace std;
typedef long long ll;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(0);

    ll N; cin >> N;
    // 2桁 => 3の倍数
    int ans = 0;
    for(int i = 10; i <= min(99LL, N); i++)
        if(i % 3 == 0) ans++;

    // 3桁以上 => 各桁の数字 in {0, 3, 6, 9}
    queue<ll> q;
    for(int d : {3, 6, 9}) q.push(d);
    while(!q.empty()) {
        ll x = q.front(); q.pop();
        for(int d : {0, 3, 6, 9}) {
            x = x * 10 + d;
            if(x <= N) {
                if(100 <= x) ans++;
                q.push(x);
            }
            x /= 10;
        }
    }
    cout << ans << endl;
}