EASY JAVA SOLUTION

public static int marsExploration(String s) { // Write your code here

    int count=0;
    for(int i=0;i<=s.length()-3;i+=3)
    {
        if(s.charAt(i)!='S')
        count++;
        if(s.charAt(i+1)!='O')
        count++;
        if(s.charAt(i+2)!='S')
        count++;
    }
    return count;

}