contract MyContract {
   // short string as it only has 31 characters
    string public exists = "thequickbrownfoxjumpsoverthelaz";
}

contract MyScript is Script {
    using stdStorage for StdStorage;

    function run() public {
        uint256 deployerPrivateKey = vm.envUint("PRIVATE_KEY");
        vm.startBroadcast(deployerPrivateKey);

        MyContract s = new MyContract();

        uint256 slot = stdstore.target(address(s)).sig("exists()").find();
        console2.log(slot);
        vm.stopBroadcast();
    }
}