func_code_string: #include <bits/stdc++.h>   using namespace std;   set<long long> s;   void dfs(int a, int b, long long sum, int d, int& n) {     if (d >= 0) {       if (sum <= n && sum > 0) {         s.insert(sum);       }     }     if (d == 0) {       return;     }     dfs(a, b, sum * 10 + a, d - 1, n);     dfs(a, b, sum * 10 + b, d - 1, n);   }   int main() {     int n;     cin >> n;     int c = 0, nn = n;     while (nn) {       nn /= 10;       ++c;     }     for (int i = 0; i <= 9; ++i) {       for (int j = i + 1; j <= 9; ++j) {         dfs(i, j, 0, c, n);       }     }     cout << s.size() << endl;   }   