**we need to find how many r mismatched with SOS so just iterate through 3 bits and check those 3 bits only **

def marsExploration(s): k=0

for i in range(0,len(s)-2,3):
    if s[i]!='S':
        k=k+1
    if s[i+1]!='O':
        k=k+1
    if s[i+2]!='S':
        k=k+1



#k=len(s)//3
return k