Var
n,i,j,k,s,t:integer;
y:longint;
a,b:array[1..100] of longint;
Begin
readln(n);
for i:=1 to n do read(a[i]);
s:=0;
for j:=1 to n-1 do
if a[j]>a[j+1] then
begin
t:=a[j]; a[j+1]:=a[j]; a[j+1]:=t;
end;
for i:=1 to n do b[i]:=0;
for i:=1 to n-1 do
for j:=i+1 to n do
begin
y:=a[i]+a[j];
for k:=1 to n do
if y:=a[k] then b[k]:=1;
end;
for i:=1 to n do
if b[i]=1 then s:=s+1;
write(s);
End.