Update the piece of code to correct the bug.
a = 6
b = 5
c = a + b
print(d)
a = 6
b = 5
c = a + b
print(c)
<sys>[INST] Update the piece of code to correct the bug. [/INST] Input:
a = 6
b = 5
c = a + b
print(d) </sys>