how to calculate 3D netcdf in matlab?

I have 300-by-240-by-365 3D netcdf file for 16 years rainfall data. I need to have mean monthly data which contains 300-by-240-by-12. how can I do this?

here is my trial script

clear all;

MP2(1:300,1:240,1:12)=0; % in case of IMERG lat is arranged in row where as lon is arranged in column((lat:lon,year)=0) is Monthly Precipitation (MP) with zero intial matrix to start for loop

for yy=2002:2017 % the year from 2002 to 2017

for mm=1:12

ap2(1:300,1:240)=0;

E = eomday(yy,mm);

dy=YYYYMMDD2doy(yy,mm,1);

hits1 = ['D:\Rainfall_Data_from_Satelite\CHIRPS/','chirps-v2.0.',num2str(yy,'%02d'),'.days_p05.nc'];

fe = dir(hits1);

ncid = netcdf.open(hits1);

lat=netcdf.getVar(ncid,0,'single'); % latitude

lon=netcdf.getVar(ncid,1,'single'); % longitude

p1=ncread(hits1,'precip',[4269,1061,dy],[300,240,E]);% days in a month

p1_sum=nansum(p1,3); % a monthly rainfall using sum of daily data

% scale=netcdf.getAtt(ncid,3,'scale_factor');

% offset=netcdf.getAtt(ncid,3,'add_offset');

netcdf.close(ncid);

end

MP2(:,:,mm)=p1_sum;

end