import sys
lb = 1
rb = 1000000000
ans = -1
while lb <= rb:
  mid = int( ( lb + rb ) / 2 )
  print ("? %d" % mid )
  sys.stdout.flush()
  res = int( input() )
  if res == 1:
    ans = mid
    lb = mid + 1
  else:
    rb = mid - 1
print("! %d" % ans)
sys.stdout.flush()