In the given circuit, there is AND, NOR and a NOT gate.
Output of AND gate: $\overline{\mathrm{A} \cdot \mathrm{B}}$
Output of NOT gate: $\overline{\mathrm{C}}$
$\therefore \quad$ The boolean expression will be:
$\overline{\mathrm{A} \cdot \mathrm{B}}+\overline{\mathrm{C}}$