0.1+0.12+0.123+0.1234+.+0.123456789
=0.1*9+0.02*8+0.003*7+0.0004*6+0.00005*5+0.000006*4+0.0000007*3
+0.00000008*2+0.000000009*1
=0.9+0.16+0.021+0.0024+0.00025+0.000024+0.0000021+0.00000016+0.000000009
=1.083676269