Graphics[{
EdgeForm[{Black, AbsoluteThickness[1.5]}],
{Lighter[Yellow],
Rectangle[{0, 0}, {2, 1}, RoundingRadius -> .6]},
{Lighter[Cyan],
Rectangle[{3, -1.25}, {5, -.25}, RoundingRadius -> .2]},
{Lighter[Yellow],
Rectangle[{3, -3}, {5, -2}, RoundingRadius -> .6]},
Arrow[{{2, .5}, {4, .5}, {4, -.25}}], Arrow[{{4, -1.25}, {4, -2}}],
Text["Input", {1, .5}], Text["f(x)", {4, -.75}],
Text["Output", {4, -2.5}]
}]