Number of perfect squares less than N?

Hint: It will be equal to the floor function of $\sqrt N$

Hint: It will be equal to the number of positive integers less than or equal to $\sqrt{N}$.

The other answers here are correct, but I would like to explain why they work. It's because the square of any whole number is greater than the squares of smaller whole numbers. For example, the square of 5 (25) is greater than the square of 4, 3, 2, and 1 (16, 9, 4, and 1, respectively). Therefore, the number of squares smaller than the square of a number, is the number of whole numbers less than it.