A brass rod $0.80\ \text{m}$ long, with a cross-section of $3.0\ \text{cm}^2$, is squeezed end to end in a press by a force of $2.7 \times 10^{4}\ \text{N}$. By how much does it shorten? ($Y = 9.0 \times 10^{10}\ \text{Pa}$.)