a)

program ct;

uses crt;

var S,i,n:integer;

begin

clrscr;

   write('nhap n;=');readln(n);

    S:=0;

      for i:=1 to n do

        if i mod 2=0 then S:=S+1/i;

    writeln('tong S=',S);

readln

end.

b)

program ct;

uses crt;

var S,i,n:integer;

begin

clrscr;

   write('nhap n;=');readln(n);

    S:=0;

      for i:=1 to n do

        if i mod 2=1then S:=S+i;

    writeln('tong S=',S);

readln

end.

uses crt;

var k,i:longint;

       S1,S2:real;

begin

clrscr;

write('Nhap so cuoi cung cua day so: ');readln(n);

S1:=0;S2:=0;

for i:= 1 to n do S1:=S1+(1/i);

for k:=1 to n do 

if k mod 2=1 then S2:=S2+(1/i);

writeln('Cau a: S1=',S1:0:2);

writeln('Cau b: S2=',S2:0:2);

readln;

end.