Xiao Qing runs 3 meters per second, Xiao Dong runs 4 meters per second, and Xiao Ming runs 2 meters per second. Three people run in the same direction from the starting line along a 600-meter circular track, and after a few seconds, the three start from the starting point at the same time.
小青每秒跑3米，小东每秒跑4米，小明每秒跑2米．三人沿600米的环形跑道从起跑线同时同向跑步，经过多少秒后三人又同时从出发点出发．
<result>600</result>