Fitter Flock

Larry and Isaac each raise a flock of $2026$ ducks, where each duck is either yellow or white. They decide to make all of their ducks take part in an obstacle course, and want to see how many ducks can complete the course without running out of stamina.

$651$ of Larry's ducks complete the race. He declares that he has the fitter flock, after all $372/987\approx 37.7\%$ of his yellow ducks completed the course, which is a higher completion rate than Isaac's yellow ducks, and $279/1039\approx 26.9\%$ of his white ducks completed the course, which is also a higher completion rate than Issac's white ducks.

Isaac has at least one yellow duck and one white duck in his flock. What is the highest number of Isaac's ducks which could have finished the course?

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The contest ended at 8:16 p.m. AEST on Thursday 2nd July. All submissions will be unofficial .