Serial.begin(int speed) Serial.begin() - Arduino Reference says
use one of these rates: 300, 1200, 2400, 4800, 9600, 14400, 19200, 28800, 38400, 57600, or 115200
Data type int int() - Arduino Reference says
This yields a range of -32,768 to 32,767
So the speeds of 38400, 57600, and 115200 don't fit. The first two will if it's an unsigned int, but even then the 115200 won't.