Sum over cell array of sparse matrices

I have 100 sparse matrices of size N by N, where N=65536.

They have about 5500000 nonzero elements(0.13% of N^2) close to the diagonal.

They are stored in a cell array, S{1}, ... , S{100}, and I want to compute the sum S{1}+...+S{100}.

Sum=sparse(N,N);
for i=1:100
    Sum=Sum+S{i};
end

The above for loop code took about 25 seconds. Is there any way to optimize this code?

Answer 1

[Stalin Samuel]

v1=[S{1:100}];
Sum=sum(v1);

[Gobi]

This code gives a 1 by N*100 vector. v1 is a matrix stacking S{:}, and just summing up is not what I want.