f = @(x)sum(cumprod(-sort(-x)>=(1:numel(x))))

f([0,0,0,0])
f([12,312,33,12])
f([1,2,3,4,5,6,7])
f([22,33,1,2,4])
f([1000,2,2,2])
f([23,42,12,92,39,46,23,56,31,12,43,23,54,23,56,73,35,73,42,12,10,15,35,23,12,42])