简单而强大

#include <iostream>
#include <algorithm>
#include <cstring>

using namespace std;

int x;
int cnt;

bool check(int x)
{
    int count = 1;

    while (x)
    {
        int t = x % 10;
        if (count % 2 == 0 && t % 2 == 1) return false;
        if (count % 2 == 1 && t % 2 == 0) return false;

        x /= 10;
        count++;
    }

    return true;
}

int main()
{
    cin >> x;
    for (int i = 1; i <= x; i++) if (check(i)) cnt++;

    cout << cnt << endl;

    return 0;
}