#!/usr/bin/env python3

import datetime
import sys

formats = (
    '%Y-%m-%d',
    '%d.%m.%Y')

for format in formats:
    try:
        day = datetime.datetime.strptime(sys.argv[1], format).date()
    except ValueError:
        continue
    print(day.isocalendar()[1])
    sys.exit(0)

print("no format matched:")
print("\n".join("  {}".format(f) for f in formats))
sys.exit(1)