int MAIN()
{
  int n;  cin>>n;
  
  if(n<10) return n;
  
  queue<LL> stq;
  for(LL i=10;i<=99&&i<=n;i++) stq.push(i);
  
  int ret = 0;
  while(!stq.empty()) {
    LL can = stq.front(); stq.pop();
    LL cansave = can;
    if(can>n) continue;
    ret++;
    
    LL a=can%10,b=-1;
    while(can>0&&(a==can%10)) can/=10;
    if(can>0) b=can%10;
  
    if(b==-1) {
      for(int k=0;k<=9;k++) stq.push(cansave*10+(LL)k);
    }else {
      stq.push(cansave*10+a);
      stq.push(cansave*10+b);
    }
  }
  
  cout<<ret+9;

  return 0;
}

int main()
{
  //srand((unsigned)time(NULL));
  #ifdef LOCAL_TEST
    freopen("in.txt", "r", stdin);
    freopen("out.txt", "w", stdout);
  #endif
  ios :: sync_with_stdio(false);
  //cout << fixed << setprecision(16);
  return MAIN();
}