foo.cc: In function 'int WeekdayOfTheFirstDay(int, int)':
foo.cc:11:9: error: 'DaysOfYear' was not declared in this scope
    sum+=DaysOfYear(y);
         ^~~~~~~~~~
foo.cc:15:9: error: 'DaysOfMonth' was not declared in this scope
    sum+=DaysOfMonth(year,m);
         ^~~~~~~~~~~

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