What is the runtime complexity of the following code?

NumberSearch$($numbers$,$ N$,$ key$)$

$\{$

mid $=0$;

low $=0$;

high $=$ N $-1$;

while $($high $>=$ low$)$

$\{$

mid $=($high $+$ low$)/2$

if $($numbers$[$mid$]<$ key$)$

low $=$ mid $+1$;

else if $($numbers$[$mid$]>$ key$)$

high $=$ mid $1$;

else

return mid

$\}$

return $-1$

$\}$