C
int verify(int input)
{
int a = input ^ 0x31;

int junk = 900;
junk *= 5;

int b = a + 20;

int temp = 100;
temp ^= 55;

int result = b * 3;

return result == 300;
}

Assume only input is tainted.
Now, determine the taint path:

input
↓
?
↓
?
↓
?
↓
comparison

And identify which variables should not be tainted at all.

@reverseengine