Description

Logo language commands can direct a turtle to crawl on the screen. This problem uses only three Logo statements: forward FD, backward BK, and repeat REPEAT, so the turtle moves back and forth along a single straight line. Given one line of a Logo command line, output the distance between the turtle and its original position (assume the screen is large enough to let the turtle move up to a distance of $10^9$).

For example:

• Input FD 100, output: $100$.
• Input FD 100 BK 150, output: $50$.
• Input REPEAT 5[FD 100 BK 50], output: $250$.
• Input REPEAT 5[FD 50 REPEAT 10[FD 100]], output: $5250$.

Input Format

One line containing a string that is a valid Logo command line as specified above.

Output Format

A single number: the distance from the turtle’s original position.

FD 100

100

Hint

The absolute value of each statement’s argument does not exceed $1000$. The output will not exceed $10^9$.

Translated by ChatGPT 5