int anagram(string s) {
    if(s.length()%2 != 0)return -1;
    unordered_map<char,int> mp1;
    unordered_map<char,int> mp2;
    int changes = 0;
    string s1 = s.substr(0,s.size()/2);
    string s2 = s.substr(s.size()/2);
    for(int i=0; i<s1.size();i++){
        mp1[s1[i]]++;
        mp2[s2[i]]++;
    }
    for(auto key : mp1){
        if(mp2.find(key.first) == mp2.end()){
            changes += key.second;
        }else if(key.second > mp2[key.first]){
            changes += key.second - mp2[key.first];
        }
    }
    return changes;
}