AOJ2617.cpp

#include <bits/stdc++.h>

#define REP(i,n) for(int i=0;i<(int)(n);i++)
#define ALL(x) (x).begin(),(x).end()

using namespace std;

typedef long long ll;
typedef long double ld;

const ld eps = 1e-9, pi = acos(-1.0);

typedef int Data;
const int len = 1 << 17;

struct BIT {
  vector<Data> data;
  BIT() : data(len, 0) {}
  void update(int i, Data value) {
    for (; i < len; i |= i+1) data[i] += value;
  }
  Data query(int i) {
    Data s = 0;
    for (; i >= 0; i = (i&(i+1))-1) s += data[i];
    return s;
  }
};

vector<int> compressor(vector<ll> c) {
  const int n = c.size();
  vector<ll> v = c;
  vector<int> res(n);
  sort(v.begin(), v.end());
  auto it = unique(ALL(v));
  REP(i,n) res[i] = lower_bound(begin(v), it, c[i]) - begin(v);
  return res;
}

int main() {
  int N;
  cin >> N;
  vector<ll> p(N), l(N), sum(N+1);
  REP(i,N) {
    cin >> p[i];
    sum[i+1] = sum[i] + p[i];
  }
  REP(i,N) cin >> l[i];
  BIT bit;
  vector<int> v = compressor(sum);
  reverse(ALL(v));
  ll res = 0;
  for (int i: v) {
    res += bit.query(i);
    bit.update(i, 1);
  }
  sort(ALL(sum));
  bool flag = true;
  REP(i,N)
    if (sum[i+1] - sum[i] < l[i]) flag = false;
  if (flag) cout << res << endl;
  else cout << -1 << endl;
  return 0;
}