The circle of fifths encoded as semitones from C: C=0, G=7, D=2, A=9, E=4, B=11, F#=6, Db=1, Ab=8, Eb=3, Bb=10, F=5. Each step moves one position clockwise around the circle (up a fifth = +7 mod 12). Given three chords in a sequence moving around the circle, predict the fourth.