local mmi, mma = math.min, math.max
local n, m = io.read("*n", "*n")
local h = {}
local edge = {}
local invedge = {}
for i = 1, n do
  h[i] = io.read("*n")
  edge[i] = {}
  invedge[i] = {}
end
for i = 1, m do
  local x, y = io.read("*n", "*n")
  table.insert(edge[x], y)
  table.insert(invedge[y], x)
end
local function solve()
  local upped = {0}
  local downed = {0}
  for i = 2, n do
    upped[i], downed[i] = -1, -1
  end
  for i = 1, n - 1 do
    for j = 1, #edge[i] do
      local dst = edge[i][j]
      if h[i] < h[dst] and 0 <= downed[i] then
        upped[dst] = mma(upped[dst], downed[i] + h[dst] - h[i])
      end
      if h[dst] < h[i] and 0 <= upped[i] then
        downed[dst] = mma(downed[dst], upped[i])
      end
      if h[dst] < h[i] and 0 <= downed[i] then
        downed[dst] = mma(downed[dst], downed[i])
      end
    end
  end
  print(mma(downed[n], upped[n]))
end
solve()
for i = 1, n do
  edge[i] = {}
  local z = n + 1 - i
  if i < z then
    h[i], h[z] = h[z], h[i]
  end
end
for i = 1, n do
  for j = 1, #invedge[i] do
    local dst = invedge[i][j]
    table.insert(edge[n + 1 - i], n + 1 - dst)
  end
end

solve()