You should always check if the key you give is public or private key. Once your coins are stolen, there is no way to recover them. Many newbies make this mistake because of being in a hurry if the airdrop has limited participants so instead of having more coins, he would end up losing all the coins he have because of that one mistake. If you wanted to join airdrops then make a wallet specifically for airdrops and then separate your wallet in which a bigger chunk of your account is being kept so that even if you mistakenly input your private key instead of public key, you still have another account and if your coins are not yet stolen then you should act fast in transferring it to another wallet. If you are lucky then you can still save your coins.