All the elements from carbon to uranium present in the Solar System were produced by hundreds to thousands of stars belonging to different stellar generations that evolved and died during the presolar evolution of the Galaxy. Using the abundances of radioactive nuclei inferred from meteoritic analysis we can date the last of these stellar additions. We have found that the last contribution of elements such as carbon and slow neutron-capture elements to the Solar System from an asymptotic giant branch star occurred 15-30 Myr before the formation of the Sun. This provides us with an upper limit of the time when the precursor material of the Solar System became isolated from the bulk of the galactic material. Interestingly, it compares well to the lifetime of high-mass molecular clouds suggesting that the Sun was born in a very large family of stars.