How to find the index of the first non-zero element in a 2-D array in simulink?

I want to find the index of the first non-zero element in a 2-D array in simulink, just like the way that 'find' command in matlab did.

For example:

u1 = [46.15 61.21; 22.5 45.3; -1 -1; -1 -1; -1 -1];

idx= find(u<0, 1)-1 The answer would be: idx= 2