Four persons Jem, Sem, Kem and Jesu participated in a race. All the four, i.e. Jem, Sem, Kem and Jesu are running with a uniform speed to get the first, second, third and fourth positions, respectively, in a 40 km race. If Jem beats Sem by 2 km and Sem beats Kem by 4 km, and Kem beats Jesu by 2 km, then by what distance does Jem beat Jesu?