We want to make a simple calculator that can add and subtract integers, and will accept arbitrarily long mathematical formulas composed of symbols +, -, and non-negative integer numbers.

Imagine you have a file formula.txt with the summation formula such as:

100 + 50 - 25 + 0 + 123 - 1 

If you redirect the file into your program, it should compute and print the answer:

$ ./calc < formula.txt 247