C++ solution:

int marsExploration(string s) { int i; int size_s = s.size(); string sub; int count = 0;

for (i=0; i<size_s; i= i+3) {
  sub = s.substr(i, 3);
  if (s[i] != 'S'){
    count++;
  } 
  if (s[i+1] != 'O'){
    count++;
  }
  if (s[i+2] != 'S'){
    count++;
  }
  // cout << "alo: " << sub <<  endl;
  // cout << "count: " << count <<  endl;
}
return count;

}