Problem of integer optimization

35*x+40*y+50*z -> min

.4*x+.5*y+.8*z >= 2

x,y,z are positive integers

When i call

> LPSolve(35*x+40*y+50*z, {x >= 0, y >= 0, z >= 0, .4*x+.5*y+.8*z >= 2}, assume = integer);
                        [135, [x = 1, y = 0, z = 2]] -- right solution