print((function (fh)
	local n,m,a = fh:read("*n"),fh:read("*n"),{}
	for i=1,n do a[i]=n+1-i end
	for _=1,m do
		local j=fh:read("*n")
		local t=a[n+1-j]
		for i=n+1-j,n-1 do a[i]=a[i+1] end a[n]=t
	end
	return a[n]
end)(io.stdin))