> length(y)
[1] 10000000
> mean(y==1i|y==1) # すべての四角形ABCD
[1] 0.42133
> mean(y==1) # 凸四角形ABCD
[1] 0.1156938
> mean(y==1i) # 凹四角形ABCD
[1] 0.3056362