Write a program that reads a 4-bit binary number from the keyboard as a string and then converts it into decimal. For example, if the input is 1100, the output should be 12. Break the string into substrings and then convert each substring to a value for a single bit. If the bits are b₀, b₁, b₂, and b₃, the decimal equivalent is 8b₀ + 4b₁ + 2b₂ + b₃.