My co-worker said: "Gotcha!".
`Gotcha` means `I got you!`
Also, I applied for DMM Skype lesson. I selected daily plan, so I'll take a lesson once a day!
料金プラン - オンライン英会話ならDMM英会話
And, I found that it is very efficient for me to learn English by `iknow`, when I'm heading to the office.