Arch Mix Arduino Schematic Help

In an attempt to figure out how to use the SW2_USR button on the Arch Mix development board, I emailed seeed’s support asking for the pin number to use in an Arduino sketch.

The reply from seeed’s support gave me a schematic that I have already looked at countless times.

I am unable to determine what pin number I should use to access the button from that schematic. It appears to me that C33 is the only information that is identifiably unique between the three button. I have also tried the variable names “USER_BUT” and “USER_BUTTON” with no positive results.

pinMode(USER_BUT, INPUT_PULLUP); // <== 'USER_BUT' was not declared in this scope
pinMode(USER_BUTTON, INPUT_PULLUP); // <== 'USER_BUTTON' was not declared in this scope
pinMode(33, INPUT_PULLUP);  // <== HARD CRASH

FYI: The Arch Mix wiki documentation says the button is pin 125 (sometimes 152) and both of those also causes a hard crash when setting the pinMode().

How do you read the schematic for the user button?
What pin number do you think it is?