Can somebody help me? I've got WA on the test №3. I've got no idea what's wrong. Please, help me.
public void solve()throws Exception{
        int n = nextInt();
        int [] a = new int[101];
        int c =0,b;
        for (int i=0;i<n;i++){
            b = nextInt();
            a[b-600]++;
        }
        for (int i=0;i<101;i++){
            c+=a[i]>>1;
        }
        out.println(c>>2);
    }