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To achieve 4 × 4 keyboard input to achieve 4 × 4 keyboard input to achieve 4 × 4 keyboard input to achieve 4 × 4 keyboard input to achieve 4 × 4 keyboard input to achieve 4 × 4 keyboard input to achieve 4 × 4 keyboard input to achieve 4 × 4 keyboard input to achieve 4 × 4 keyboard input to achieve 4 × 4 keyboard input to achieve 4 × 4 keyboard input to achieve 4 × 4 keyboard input