Jerry starts at -1 on the real number line. He tosses a fair coin 7 times. When he gets heads, he moves 1 unit in the positive direction. When he gets tails, he moves 1 unit in the negative direction. The probability that he reaches 2 at some time during this process is $\frac{a}{b}$, where $a$ and $b$ are relatively prime positive integers. What is $a+b$?