print((function (f)
	local n,m,a = f(),f(),{}
	for i=1,n do a[i]=n+1-i end
	for _=1,m do
		local j=f()
		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)((function ()
	local M=require'ffi'
	local C,c=M.C,M.new("int[1]")
	M.cdef 'int scanf(const char*, ...);'
	return function () C.scanf("%d",c) return c[0] end
end)()))