Cycles

There are 3 cycles x, y and z for every person and they have periods of lengths 23, 28, and 33 days, resp. There is one peak in each period of a cycle. At the peak of a cycle, a person performs at his or her best in the corresponding field (x,y,z). The peaks of these 3 cycles occur at different times as the periods differ. We would like to determine when a triple peak occurs (the peaks of all 3 cy