int alternatingCharacters(string s) {
    if (s.find_first_not_of(s[0]) == string::npos) return s.size()-1;
    
    int del = 0;
    int len = s.size();
    
    for(int i = 0; i<len; i++){
        
        if((i+1)<len && s[i]==s[i+1]){
            del++;
        }
        
    }  
    
    return del;
}