找规律

#include<bits/stdc++.h>
using namespace std;
int main(){
    string s; cin >> s;
    if(s.size() == 1) cout << s;
    else{
    	bool f = 0;
        for(int i = 0;i < s.size();i++){
        	if(s[i] != '9'){
            	f = 1;
                if(i == s.size() - 1) cout << s;
                else{
                    for(int j = 1;j <= s.size() - 1;j++) cout << 9;
                }
                break;
            }
        }
        if(f == 0) cout << s;
    }
    return 0;
}