Use this and you got AC!
  Answer(n,m)=abs( Answer(1,n)-Answer(1,m) )

check this(130 tests) and YOU got AC (I think)
(N M Answer)
1 1 0
1 2 0
1 3 0
1 4 1
1 5 2
1 6 2
1 7 2
1 8 4
1 9 6
1 10 6
1 11 6
1 12 7
1 13 8
1 14 8
1 15 8
1 16 11
1 17 14
1 18 14
1 19 14
1 20 15
1 21 16
1 22 16
1 23 16
1 24 18
1 25 20
1 26 20
1 27 20
1 28 21
1 29 22
1 30 22
1 31 22
1 32 26
1 33 30
1 34 30
1 35 30
1 36 31
1 37 32
1 38 32
1 39 32
1 40 34
1 41 36
1 42 36
1 43 36
1 44 37
1 45 38
1 46 38
1 47 38
1 48 41
1 49 44
1 50 44
1 51 44
1 52 45
1 53 46
1 54 46
1 55 46
1 56 48
1 57 50
1 58 50
1 59 50
1 60 51
1 61 52
1 62 52
1 63 52
1 64 57
1 65 62
1 66 62
1 67 62
1 68 63
1 69 64
1 70 64
1 71 64
1 72 66
1 73 68
1 74 68
1 75 68
1 76 69
1 77 70
1 78 70
1 79 70
1 80 73
1 81 76
1 82 76
1 83 76
1 84 77
1 85 78
1 86 78
1 87 78
1 88 80
1 89 82
1 90 82
1 91 82
1 92 83
1 93 84
1 94 84
1 95 84
1 96 88
1 97 92
1 98 92
1 99 92
1 100 93
1 101 94
1 102 94
1 103 94
1 104 96
1 105 98
1 106 98
1 107 98
1 108 99
1 109 100
1 110 100
1 111 100
1 112 103
1 113 106
1 114 106
1 115 106
1 116 107
1 117 108
1 118 108
1 119 108
1 120 110
1 121 112
1 122 112
1 123 112
1 124 113
1 125 114
1 126 114
1 127 114
1 128 120
1 129 126
1 130 126

I think big test is also useful:
1 2147483647 2147483586

Also usefull tests:
WA 8:
4 12 (answer = 6)
WA 18:
7 9 (answer = 4)