Herw my java code:

public static int marsExploration(String s) {
 int    count = 0;
char[] ch = s.toCharArray();
for(int i=0; i<s.length(); i+=3) {
    if(ch[i] !='S')
        count++;
    if(ch[i+1] !='O')
        count++;
    if(ch[i+2] !='S')
       count++;
}
return count;
}