ai lgx , cu x>0.
daca x <10 => [lgx] =0
daca 9<x<10^2 => [lgx]=1
daca 99<x<10^3 => [lgx]=2
daca 999<x<10^4 => [lgx]=3
deci impartim S pe grupe:
S=( [lg1] +...+[lg9] ) +([lg10]+...+lg[99]) +([lg100]+...+[lg999])+([lg1000]+...+lg[2015])=>
=> S= 0 + 1*90 +2*900 +3*1016=>
=>S=90+1800+3048=4938
