_Follow along with this video:_ --- ### Bringing It Back To HorseStore Ok! With everything we've just learnt firmly understood, lets return to our `HorseStore.huff` contract. ```js #define macro MAIN() = takes(0) returns(0) { 0x00 // [0] calldataload // [calldata (32)] } ``` The `calldata` we've added to our stack is the first 32 bytes of the `calldata` sent to our contract. ``` 0xe026c01700000000000000000000000000000000000000000000000000000000 ``` We only need the `function selector`, or the first 4 bytes. In order to isolate this section of the `calldata` we will need to utilize `shr` to shift 28 bytes to the right. > **Remember:** `shr` takes the number of _bits_ to shift. 28 x 8 = 224 bits. Use `cast --to-base 224 hex` to glean that this number is `0xe0` in hexadecimal format. With that determined, let's add what we need to our contract. ```js #define macro MAIN() = takes(0) returns(0) { 0x00 // [0] calldataload // [calldata (32)] 0xe0 // [0xe0, calldata (32)] } ``` And our stack should look like this: ::image{src='/formal-verification-1/16-shr-calldata/shr-calldata-1.png' style='width: 100%; height: auto;'} Our final step to isolate the `function selector` from our received `call data` is going to be executing the `shr` operation, exciting! ```js #define macro MAIN() = takes(0) returns(0) { 0x00 // [0] calldataload // [calldata (32)] 0xe0 // [0xe0, calldata (32)] shr // [function_selector] } ``` The stack now: ::image{src='/formal-verification-1/16-shr-calldata/shr-calldata-2.png' style='width: 100%; height: auto;'} This is great! We finally have our `function selector` on the stack and we can finally start to do some function dispatching! See you in the next one!