Why do I get NZEC error in KNIGHTMV

I am not able to figure out why am i getting a NZEC error. If possible please help me in this case.Here is my code to the question KNIGHTMV

The problem is when the length of input string is less than 5, and if input is “s” you are accessing char at 2 then it is Runtime Error resulting in NZEC. Now it’s your turn to code it up!