int validSize(string s, char first, char second){
    string ans = "";
    for(int i = 0; i < s.size(); i++){
        if(s[i] == first || s[i] == second){
            if(ans.size() > 0 && ans[ans.size() - 1] == s[i]) return 0;
            else ans+=s[i];
        }
    }
    if(ans.size() < 2) return 0;
    return ans.size();
}

int alternate(string s) {
    int ans = 0;
    for(char i = 'a'; i < 'z'; i++){
        for(char j = i + 1; j <= 'z'; j++){
           int r = validSize(s, i, j);
           if(r > ans) ans = r;
        }
    }
    return ans;
}