(8*4-2)*10^0=30
              ...     (ends in 0),

   ((8*4-2)*10^0+(3*4-5)*10^1)=100
              ...     (ends in 00 and is not less than 10^2)

   ((8*4-2)*10^0+(3*4-5)*10^1+(7*4-9)*10^2)=2000
              ...     (ends in 00 and is not less than 10^3)

     etc.