必对

#include <bits/stdc++.h>
using namespace std;

int main(){
string s;
cin >> s;
int n = s.size();
int idx = -1;
for(int i = 0; i < n; i ++ ){
if(s[i] != '9'){
idx = i;
break;
}
}
if(idx == n - 1 || n == 1 || idx == -1){
cout << s;
}else{
n --;
while(n -- ) cout << 9;
}
return 0;
}