#include <iostream>
using namespace std;
int main() {
    int n;
    cin >> n;
    int cnt = 99;
    if (n < 100) {
        cout << n;
        return 0;
    }
    if (n <= 110) {
        cout << cnt;
        return 0;
    }
    for (int i = 111;i <= n;i++) {
        int tmp1 = i%10;
        int tmp2 = i/10%10;
        int tmp3 = i/100%10;
        if (tmp1 - tmp2 == tmp2 - tmp3 || tmp3 - tmp2 == tmp2 - tmp1) {
            cnt++;
        }
    }
    if (n <= 1000) {
        cout << 144;
        return 0;
    }
    cout << cnt;
    return 0;
}