def marsExploration(s):
    # Write your code here
    count = 0
    i = 0
    while i < len(s):
        if s[i] != "S":
            count +=1
        if s[i+1] != "O":
            count +=1
        if s[i+2] != "S":
            count +=1
        i += 3
    return count