# Ces programmes sont sous licence CeCILL-B V1.

def echange (x,y):
  z = x[0]
  x[0] = y[0]
  y[0] = z

a = [0 for i in range(0,2)]
a[0] = 4
b = [0 for i in range(0,2)]
b[0] = 7
echange(a,b)
print(a[0],end="")
print(" ",end="")
print(b[0])