problem 1000
problem 1001
problem 1014
problem 1020
problem 1196
problem 1243
problem 1005
problem 1327
problem 1263
problem 1264
problem 1293
problem 1409
problem 1493
problem 1496
problem 1502
problem 1545
problem 1567
problem 1712
problem 1785
problem 1877