Variable issues

I'm trying to set up a variable which every second subtracts by 1 and when it reaches zero, says "Game Over". My object is a piece of text which starts at 80 and I want it to, when it subtracts from one, to go down from 80. So in an example;

Number is 80

Variable subtracts by one every second

Set Text to 79

Please help! :/

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Thanks a ton, that really helps! (I'm on a deadline for my game and I got to get it done soon)