Can anyone say, what is wrong in my solution?

public class T1779 {
    public static void main(String[] args) throws IOException {
        BufferedReader in=new BufferedReader(new InputStreamReader(System.in));
        PrintWriter out=new PrintWriter(System.out);
        int n=Integer.parseInt(in.readLine());
        int sum=0;
        for(int i=0; i<n/2; i++){
            for(int j=n-i-1; j<n; j++){
                if(i!=j){
                    out.println((i+1)+" "+(j+1));
                    sum++;
                }
            }
        }
        System.out.println(sum);
        out.close();

    }
}

Repalce the conditions i != j with i < j because you print some edges twice.
Sorry for my bad English