$500 \text{th} ~ \text{Problem!}$

Looking at the units column, clearly $G = 0$ and there is no carry to the tens column. Now ignore the units column, and remember that none of the digits may be 0 (since it's used for $G$ ).

There are 9 letters and 9 digits, so all digits get used. Adding up all the digits gives $M+A+S+W+E+I+P+H+Y$ , which must be equal to $1+2+3+4+5+6+7+8+9 = 45$ . Now consider the addition modulo 9. $\overline{MAS} + \overline{WEI} + \overline{PHY} \equiv 45 \pmod 9$ , since we can obtain the remainder modulo 9 by adding up the digits. However, $\overline{MAS} + \overline{WEI} = \overline{PHY}$ , so we have $2 \cdot \overline{PHY} \equiv 45 \equiv 0 \pmod 9$ and so $\overline{PHY} \equiv 0 \pmod 9$ . In other words, $\overline{PHY}$ is divisible by 9. The largest possible number for $\overline{PHY}$ is hence 981, and the largest possible $S$ after this is 7, giving $\max \overline{PHYS} = \boxed{9817}$ . This is achievable, by for example $3277 + 6540 = 9817$ .