class Hamming:
def __init__(self,a,b):
self.a=a
self.b=b
def __str__(self):
cnt = 0
for i in range(len(self.a)):
if a[i] != b[i]:
cnt+=1
return "Hamming distance is {}.".format(cnt)
if __name__ == "__main__":
for i in range(int(input())):
a=input()
b=input()
C= Hamming(a,b)
print(C)