Top panel: mass evolution of the runaway star (M_max(t)∕M_ini) in a cluster with N = 5000 stars. Each of these stars has an initial mass of M_star = 2M_⊙ and an initial radius of R_star = 200R_⊙. Middle panel: the number of collisions in bins of 5 crossing times (N_col) as function of the crossing time of the cluster is shown. The red line is the best Gaussian fit. Bottom panel: the mass growth rate d M∕dt in calculated in bins of 5 crossing times is shown.