#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

vector<long long> v;
void make(long long now) {
    int digit = to_string(now).length();
    if (digit > 9)return;
    if (digit >= 3)v.push_back(now);

    now *= 10;
    make(now + 0), make(now + 3), make(now + 6), make(now + 9);
}

int main() {
    int n;
    cin >> n;

    int ret = 0;
    for (int i = 10; i <= min(99, n); i++) {
        if (i % 3 == 0)ret++;
    }

    make(3), make(6), make(9);

    for (auto &x:v) {
        if (x <= n)ret++;
    }

    cout << ret << endl;
    return 0;
}