Problem p02665 (C++)

Buggy submission (status: Runtime Error):
#define _CRT_SECURE_NO_WARNINGS
#include <algorithm>
#include <functional>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <string>
#include <vector>
#define _USE_MATH_DEFINES
#include <bitset>
#include <deque>
#include <iostream>
#include <list>
#include <map>
#include <math.h>
#include <queue>
#include <set>
using namespace std;
typedef long long ll;
#define rep(i, a, b) for (auto i = a; i < b; i++)
#define all(_x) _x.begin(), _x.end()
#define r_sort(_x) sort(_x.begin(), _x.end(), std::greater<int>())
#define vec_cnt(_a, _n) (upper_bound(all(_a), _n) - lower_bound(all(_a), _n))
#define vec_unique(_a) _a.erase(std::unique(all(_a)), _a.end());
#define vvec vector<vector<ll>>
ll gcd(ll a, ll b) { return a % b == 0 ? b : gcd(b, a % b); }
ll lcm(ll a, ll b) { return (a / gcd(a, b)) * b; }
#define INF 1 << 30
const int mod = 1000000007;
ll power(ll x, ll p) {
  ll a = 1;
  while (p > 0) {
    if (p % 2 == 0) {
      x *= x;
      p /= 2;
    } else {
      a *= x;
      p--;
    }
  }
  return a;
}
ll mpower(ll x, ll p) {
  ll a = 1;
  while (p > 0) {
    if (p % 2 == 0) {
      x = x * x % mod;
      p /= 2;
    } else {
      a = a * x % mod;
      p--;
    }
  }
  return a;
}
ll ac(ll n, ll k) {
  ll a = 1;
  rep(i, 1, k) {
    a *= n - i + 1;
    a /= i;
  }
  return a;
}
ll mc(ll n, ll m) {
  ll k = 1, l = 1;
  rep(i, n - m + 1, n + 1) k = k * i % mod;
  rep(i, 1, m + 1) l = l * i % mod;
  l = mpower(l, mod - 2);
  return k * l % mod;
}

int main() {
  ll n, i;
  cin >> n;
  vector<ll> a(n + 1), l(n + 1), r(n + 1);
  rep(i, 0, n + 1) cin >> a[i];
  l[n] = r[n] = a[n];
  for (i = n - 1; i >= 0ll; i--) {
    l[i] = a[i] + (l[i + 1] + 1) / 2;
    r[i] = a[i] + r[i + 1];
  }
  if (l[0] > 1)
    return puts("-1");
  ll c = 1, ans = 0;
  for (i = 0ll; i < n; i++) {
    ans += c;
    c -= a[i];
    c = min(c * 2, r[i + 1]);
  }
  printf("%lld\n", ans + c);
  return 0;
}


Fixed submission:
#define _CRT_SECURE_NO_WARNINGS
#include <algorithm>
#include <functional>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <string>
#include <vector>
#define _USE_MATH_DEFINES
#include <bitset>
#include <deque>
#include <iostream>
#include <list>
#include <map>
#include <math.h>
#include <queue>
#include <set>
using namespace std;
typedef long long ll;
#define rep(i, a, b) for (auto i = a; i < b; i++)
#define all(_x) _x.begin(), _x.end()
#define r_sort(_x) sort(_x.begin(), _x.end(), std::greater<int>())
#define vec_cnt(_a, _n) (upper_bound(all(_a), _n) - lower_bound(all(_a), _n))
#define vec_unique(_a) _a.erase(std::unique(all(_a)), _a.end());
#define vvec vector<vector<ll>>
ll gcd(ll a, ll b) { return a % b == 0 ? b : gcd(b, a % b); }
ll lcm(ll a, ll b) { return (a / gcd(a, b)) * b; }
#define INF 1 << 30
const int mod = 1000000007;
ll power(ll x, ll p) {
  ll a = 1;
  while (p > 0) {
    if (p % 2 == 0) {
      x *= x;
      p /= 2;
    } else {
      a *= x;
      p--;
    }
  }
  return a;
}
ll mpower(ll x, ll p) {
  ll a = 1;
  while (p > 0) {
    if (p % 2 == 0) {
      x = x * x % mod;
      p /= 2;
    } else {
      a = a * x % mod;
      p--;
    }
  }
  return a;
}
ll ac(ll n, ll k) {
  ll a = 1;
  rep(i, 1, k) {
    a *= n - i + 1;
    a /= i;
  }
  return a;
}
ll mc(ll n, ll m) {
  ll k = 1, l = 1;
  rep(i, n - m + 1, n + 1) k = k * i % mod;
  rep(i, 1, m + 1) l = l * i % mod;
  l = mpower(l, mod - 2);
  return k * l % mod;
}

int main() {
  ll n, i;
  cin >> n;
  vector<ll> a(n + 1), l(n + 1), r(n + 1);
  rep(i, 0, n + 1) cin >> a[i];
  l[n] = r[n] = a[n];
  for (i = n - 1; i >= 0ll; i--) {
    l[i] = a[i] + (l[i + 1] + 1) / 2;
    r[i] = a[i] + r[i + 1];
  }
  if (l[0] > 1ll) {
    puts("-1");
    return 0;
  }
  ll c = 1, ans = 0;
  for (i = 0ll; i < n; i++) {
    ans += c;
    c -= a[i];
    c = min(c * 2, r[i + 1]);
  }
  printf("%lld\n", ans + c);
  return 0;
}