How to limit user input with do while loop, for loop or if.

I'm trying to make a program, but am unsure how to stop the user from enter a number smaller than what i want. I'm want to use an if, while or do-while loop. Any Ideas?

I know user input, but don't really know while or if. Any help would be great.

cout << "How many rocks do you want from the ground? You can choose for 5 or more."; cin >> rockPile;