set.seed(515)
u = c(1,1,1,0,0,0,0);  m = 10^6
nr.r = replicate(m,  sum(c(sample(u, 2),sample(u, 2))))
table(nr.r)/m
nr.r
       0        1        2        3        4
 0.081424 0.326159 0.408962 0.163044 0.020411