local n = io.read("*n")
local m = io.read("*n")
local t = {}
local lim = 100000
for i = 1, lim do
  t[i] = false
end
for i = 1, m do
  local a, b = io.read("*n", "*n")
  b = (b + a * 100010) % a
  if t[a] then
    if t[a] ~= b then
      print("NaN") os.exit()
    end
  else
    t[a] = b
  end
end
do
  local f = true
  for i = 1, lim do
    if t[i] and t[i] ~= 0 then
      f = false
      break
    end
  end
  if f then
    print(0) os.exit()
  end
end
local f = {}
for i = 1, n do
  f[i] = 0
end

local need = 0
for i = 1, lim do
  if t[i] then
    need = need + 1
    local b = t[i]
    local v = b
    if v == 0 then v = i end
    while v <= n do
      f[v] = f[v] + 1
      v = v + i
    end
  end
end
for i = 1, n do
  if f[i] == need then
    print(i) os.exit()
  end
end
print("NaN")