[백준] 3449

import sys
for _ in range(int(sys.stdin.readline())):
    tmp=sys.stdin.readline()
    tmp2=sys.stdin.readline()
    hamdistance=0
    for i in range(len(tmp)-1):
        if int (tmp[i])- int (tmp2[i])!=0: hamdistance+=1
    print("Hamming distance is %d."%hamdistance)