def marsExploration(s):
    altered_count = 0
    for i in range(0, len(s), 3):
        if s[i] != 'S':
            altered_count += 1
        if s[i + 1] != 'O':
            altered_count += 1
        if s[i + 2] != 'S':
            altered_count += 1
    return altered_count