var v:array[1..9000] of integer;
n,nr,i,j,k:longint;
f:text;
begin
assign(f,'medie.in');reset(f);
read(f,n);
for i:=1 to n do read(f,v[i]);
nr:=0;
for i:=1 to n do begin
    for j:=1 to n do
        for k:=1 to j-1 do
            if (2*v[i]=v[j]+v[k])and (i<>j) and (i<>k) and(j<>k) and ((v[j]+v[k]) mod 2=0) then inc(nr);
            end;
assign(f,'medie.out');rewrite(f);
write(f,nr);
close(f);
end.