longsum(long x){ long ret = 0; while(x > 0) { ret += tr[x]; x -= lowbit(x); } return ret; }
intmain(){ int n; cin >> n; for(int i = 1; i <= n; i++) { cin >> a[i]; } long ret = 0; for(int i = 1; i <= n; i++) { ret += sum(a[i] + i - 1); add(a[i] + i); } cout << ret << endl; return0; }