log2（log3(log4x)=0
（log3(log4x)=2^0=1
log4x=3^1=3
x=4^3=64
log3（log4(log2y)=0
log4(log2y)=3^0=1
log2y=4^1=4
y=2^4=16
log4（log2(log3z)=0
log2(log3z)=4^0=1
log3z=2^1=2
z=3^2=9
所以x+y-z=64+16-9=71