import sys

ontrain = 0
x = sys.stdin.readline()
y = x.split()
cap = int(y[0])
b = int(y[1])

for i in range(0, b):
  z = sys.stdin.readline()
  g = z.split()
  left = int(g[0])
  enter = int(g[1])
  stay = int(g[2])

  if left > ontrain:
      print("impossible")
      break

  if enter+ontrain > cap+1:
      print("impossible")
      break
  else:
      ontrain += enter
      ontrain -= left

  space = cap-ontrain

  if i == b-1 and ontrain > 0:
   print("impossible")
   break
  elif i == b-1 and stay > 0:
    print("impossible")
    break
  elif stay > space+1:
    print("impossible")
    break
  elif i == b-1:
   print("possible")
   break