program Zadacha4;

{$APPTYPE CONSOLE}

var
a:array [1..25] of integer;
i,s:integer;
begin
s:=0;
for i:=1 to 25 do readln(a[i]);
for i:=1 to 25 do
if i mod 2=1 then s:=s+a[i];
writeln(s);
readln;
readln;
end.