Which XXX and YYY will output the sum of the input integers $($stopping when $-1$ is input$)?$

Flowchart has $2$ variables $($integer val, integer sum$)$ and $8$ nodes. Node $1$ is the start node and points to node $2.$ Node $2$ code: val $=$ Get next input Node $2$ points to node $3.$ Node $3$ code: XXX Node $3$ points to node $4.$ Node $4$ code: while not$($val $==-1)$ Node $4$ points to nodes $5($condition is true$)$ and $7($condition is false$).$ Node $5$ code: YYY Node $5$ points to node $6.$ Node $6$ code: val $=$ Get next input Node $6$ points to node $4.$ Node $7$ code: Put sum to output Node $7$ points to node $8.$ Node $8$ is the end node.

a$.$

XXX: sum $=$ val $/$ YYY: sum $=$ val

b$.$

XXX: sum $=$ val $/$ YYY: sum $=$ sum $+$ val

c$.$

XXX: sum $=0/$ YYY: sum $=$ sum $+$ val

d$.$

XXX: sum $=0/$ YYY: sum $=$ val