program loop
integer row, col
integer mat(2,2)
integer sum
mat (1, 1) = 1
mat (1, 2) = 2
mat (2, 1) = 3
mat (2, 2) = 4
sum = 0
Do row = 1, 2, 1
Do col = 1, 2, 1
if (mat(row, col) == 0) exit
sum = sum + mat(row, col)
End Do
End Do
print *, sum
end program loop
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