import sys

left=10
right=1000000001
print "? %d" % 512
sys.stdout.flush()
res=int(raw_input())
if res>0:
    left=513
elif res<0:
    right=511
else:
    print "! %d" % 512
    sys.stdout.flush()
    exit()

t=1
while left < right:
    mid=(left+right)/2
    print "? %d" % (mid-t)
    sys.stdout.flush()
    res=int(raw_input())
    if res>0:
        left=mid+1
    elif res<0:
        right=mid-1
    else:
        left=right=mid
    t+=1
print "! %d" % left
sys.stdout.flush()