Input X contains NaN.

"NaN" stands for "Not a Number" and is usually encountered in mathematical operations where the result is undefined or cannot be represented as a numerical value.

To handle this error in code, you can use conditional statements to check for NaN before performing any calculations. For example, in Python, you can use the `math.isnan()` function to check if a value is NaN:

import math

x = float(input("Enter a number: "))

if math.isnan(x):
    print("Input contains NaN")
else:
    # perform calculations

Alternatively, you can use try-except blocks to catch any exceptions that may arise from NaN values:

x = float(input("Enter a number: "))

try:
    # perform calculations
except ValueError:
    print("Input contains NaN")