import sys
watermark = 0
with open('blocknumbers') as f:
    current = int(f.readline())
    if(current % 1000 == 0):
        print(current)
    if not (watermark + 1 == int(current)):
        print("inconsistency at " + str(watermark) + ", " + str(current));
        sys.exit(-1)
    watermark = current