var a:array[1..100,1..100] of integer;
i,j,s,n,k:integer;
Begin
read(n);
for i:= 1 to n do
for j:= 1 to n do begin
read(a[i,j]);
if i mod 2=0 then begin
k:=k+1;
s:=s+a[i,j];
end;
writeln(s/k);
end.
var a:array[1..100,1..100] of integer;
i,j,s,n,k:integer;
Begin
read(n);
for i:= 1 to n do
for j:= 1 to n do begin
read(a[i,j]);
if i mod 2=0 then begin
k:=k+1;
s:=s+a[i,j];
end;
end;
writeln(s/k);
end.