Cash per second rapidly going up

if(coalMine >= 1) {
cashPerSecond += coalMine;
}

I have this, but now every few miliseconds my cash per second goes up by one which increases my cash alot. I just want it to go up ONCE! Not all the time, I want it once. Thank you
-Ryan

if(coalMine >= 1) {
cashPerSecond += coalMine;
coalMine = 0;
}

Now the if statement will be false in the next Update/FixedUpdate call.