24.已知圆O:x2+y2=4O:x^{2}+y^{2}=4O:x2+y2=4与圆C:(x−1)2+(y−3)2=4C:(x-1)^{2}+(y-3)^{2}=4C:(x−1)2+(y−3)2=4,直线l:2x−y+4=0l:2x-y+4=0l:2x−y+4=0交圆OOO于AAA,BBB两点,交圆CCC于DDD,EEE两点,MMM,NNN分别为ABABAB,DEDEDE的中点,则∣MN∣=\vert MN\vert =∣MN∣=___755\frac{7\sqrt{5}}{5}575___.