In the snippet of MIPS assembler code below, how many times is instruction memory accessed? How many times is data memory accessed? (Count only accesses to memory, not registers.)

lw $v1, 0($a0)

lw $v0, 4($a0)

addi $v1, $v1, 1

sw $v1, 0($a0)

addi $a0, $a0, 4

sub $v0, $v0, $v1

sw $v0, 0($a0)