var a: array[1..20] of integer; i: byte; tong1, tong2: real;
begin
    for i:=1 to 20 do
    begin
        write('Nhap gia tri cho phan tu thu ',i,': ');
        readln(a[i]);
    end;
    for i:=1 to 20 do
        if (a[i] mod 5 = 0) then tong1:=tong1+a[i];
    writeln('Ket qua: ');
    writeln('Cau a: ',tong1:0:0);
    for i:=1 to 20 do
        if (a[i] = 4) then a[i]:= 6;
    writeln('Cau b: Day la mang moi sau khi thay the.');
    for i:=1 to 20 do
        write(a[i],' ');
    writeln();
    writeln('Cau c: Chi so cac phan tu le la (neu khong co so nao, day nay khong co so le):');
    for i:=1 to 20 do
        if (a[i] mod 2 = 1) then write(i,' ');
    writeln();
    for i:=1 to 20 do
        if (a[i] mod 3 = 0) then tong2:=tong2+1;
    writeln('Cau c: So luong so chia het cho 3 la:',tong2:0:0);
    readln
end.