Whether you request optimization or not, the compiler may determine that an expression that is to be output may be calculated entirely at compile time, store that value in the EXE/a.out, and simply output that previously computed value.
Obviously, the result of the first loop is N+4, and it appears that the Intel compiler did not have to place code in the executable to calculate that result (elapsed time = 0).
We have seen an extreme example of such compile time calculation in a recent thread.