initial begin
        program_memory[0] = 20'b00000000000000000001;
        program_memory[1] = 20'b00001000000000000010;
        program_memory[2] = 20'b00010000000000000110;
        program_memory[3] = 20'b10010100100000000101;
        program_memory[4] = 20'b10000001100000001000;
        program_memory[5] = 20'b01010000001000000000;
        program_memory[6] = 20'b01100001000000000001;
        program_memory[7] = 20'b10000001100000000011;
        program_memory[8] = 20'b10000001110000000000;
    end