public static int marsExploration(string s)
    {
        s = s.ToUpper();
        
        int count = 0;
        string messageSig = "SOS";
        
        int longitud = s.Length;
        var modules = new List<string>();
        
        if((longitud < 1 || longitud > 99) && longitud % 3 != 0) throw new InvalidDataException("Longitud invalida");
        
        for(int i = 0; i < longitud; i += 3){
            modules.Add(s.Substring(i, 3));
        }
        
        foreach(string subMessage in modules){
            for(int j = 0; j < 3; j++){
                if(subMessage[j] != messageSig[j]) count++;
            }
        }
        
        return count;
    }

def marsExploration(s):
    nChanged = 0
    for i, value in enumerate(s):
        remainder =  i % 3
        if remainder in (0, 2) and value != "S":
            nChanged += 1
        elif remainder == 1 and value != "O":
            nChanged += 1
    return nChanged

func marsExploration(s: String) -> Int {
    var changed = 0
    for (index, c) in s.enumerated() {
        switch index % 3 {
            case 0, 2:
               if c != "S" {
                    changed = changed + 1
               }
            case 1:
                if c != "O" {
                    changed = changed + 1
               }
            default:
                break
        }
    }
    return changed
}

  public static int marsExploration(String s) {
        
        int counter = 0;
        int position = 1;
        for(int i = 0; i < s.length(); i++){            
            System.out.println(position);
            
            if((position == 1 || position == 3) && s.charAt(i) != 'S') {
            counter++;
            }else if(position == 2 && s.charAt(i) != 'O'){
            counter++;
            }   
            
            if(position == 3){
                position = 1;
            }else{
                position++;
            }                                                                                                                                            
        }
        
        return counter;
    }

def marsExploration(s):
    sos = "SOS" * (len(s)//3)
    changed = 0
    for index, item in enumerate(s):
        if item != sos[index]:
            changed += 1
    return changed