program phuongt; uses crt; var s, n, i: integer; begin clrscr; write('Nhap n = '); readln(n); n:=3*n; i:=3; while i<=n do begin if i mod 3 = 0 then s:=s+i; i:=i+1; end; write('S = ', s); readln
uses crt; var n,i,s:integer; begin clrscr; i:=0; write('Nhap n: '); readln(n); n:=n*3; while i<=n do begin inc(s,i); inc(i,3); end; write(s); readln; end.
