local ffi = require 'ffi'
local C = ffi.C
ffi.cdef 'int getchar_unlocked(void);'

print((function (f, g)
	return f(g(8)) and "YES" or "NO"
end)(function (r)
	local x,y,n,a,b=r(),r(),r(),r(),0
	for i=2,n do b=r() if a*y>b*x then return false end a=b end
	return true
end, function (n)
        local a = ffi.new('uint8_t[?]',n)
        return function ()
                for i=0,n do
                        a[i]=C.getchar_unlocked()
                        if a[i]==32 or a[i]==10 then a[i]=0 break end
                end
                return tonumber(ffi.string(a))
        end
end))