If `veca,vecb,vecc` are unit vectors such that `veca` is perpendicular to

If `veca,vecb,vecc` are unit vectors such that `veca` is perpendicular to the plane `vecb` and `vecc` and angle between `vecb` and `vecc` is `(pi)/(3)`, than value of `|veca+vecb+vecc|` is