1323. Maximum 69 Number

You are given a positive integer num consisting only of digits 6 and 9.

Return the maximum number you can get by changing at most one digit (6 becomes 9, and 9 becomes 6).

class Solution {
public:
    int maximum69Number (int num) {
       string s = to_string(num);
        for(int i = 0; i < s.length(); i++) {
            if(s[i] == '6') {
                s[i] = '9';
                return stoi(s);
            }
        }
        return num;
    }
};