// Sea, You & Me
#include<bits/stdc++.h>
#define LL long long
#define DB double
#define MOD 1000000007
#define ls(x) (x << 1)
#define rs(x) (x << 1 | 1)
#define lowbit(x) ((-x) & x)
#define MP make_pair
#define MT make_tuple
#define VI vector<int>
#define VL vector<LL>
#define VII VI::iterator
#define VLI VL::iterator
#define all(x) x.begin(), x.end()
#define EB emplace_back
#define PII pair<int, int>
#define SI set<int>
#define SII SI::iterator
#define fi first
#define se second
using namespace std;
template<typename T> void chkmn(T &a, const T b) { (a > b) && (a = b); }
template<typename T> void chkmx(T &a, const T b) { (a < b) && (a = b); }
void Inc(int &a, const int &b) { ((a += b) >= MOD) && (a -= MOD); }
void Dec(int &a, const int &b) { ((a -= b) < 0) && (a += MOD); }
void Mul(int &a, const int &b) { a = 1LL * a * b % MOD; }
void Sqr(int &a) { a = 1LL * a * a % MOD; }
int inc(const int &a, const int &b) { return (a + b >= MOD) ? a + b - MOD : a + b; }
int dec(const int &a, const int &b) { return (a - b < 0) ? a - b + MOD : a - b; }
int mul(const int &a, const int &b) { return 1LL * a * b % MOD; }
int sqr(const int &a) { return 1LL * a * a % MOD; }
int qwqmi(int x, int k = MOD - 2)
{
	int res = 1;
	while(k)
	{
		if(k & 1) Mul(res, x);
		k >>= 1, Sqr(x);
	}
	return res;
}
template<typename T> void read(T &x)
{
	x = 0;
	int f = 1;
	char ch = getchar();
	while(!isdigit(ch))
	{
		if(ch == '-')
			f = -1;
		ch = getchar();
	}
	while(isdigit(ch))
	{
		x = (x << 1) + (x << 3) + (ch ^ 48);
		ch = getchar();
	}
	x = x * f;
}
const int N = 1e5 + 5;
int n; LL a[N << 2], w[N << 2];
bool check(int x)
{
	for(int i = 0; i < n; ++i)
		w[i] = a[i];
	LL cnt = 1;
	for(int i = x; i < n; ++i)
		w[0] += w[i];
	for(int i = x - 1; i >= 0; --i)
	{
		LL z = w[i] - cnt;
		if(z > 0) w[0] += z;
		if(z < 0) cnt += -z;
//		if(i == x - 20) cerr << "cnt : " << cnt << '\n';
	}
//	cerr << "cnt : " << cnt << '\n';
	return w[0] >= cnt;
}
int main()
{
	read(n);
	LL sum = 0;
	for(int i = 0; i < n; ++i)
		read(a[i]), sum += a[i];
	if(sum == 1) for(int i = 0; i < n; ++i)
		if(a[i] == 1) return printf("%d\n", i), 0;
	int l = 1, r = n + 30, res = 0;
	while(l <= r)
	{
		int mid = (l + r) / 2;
		if(check(mid)) 
			res = mid, l = mid + 1;
		else r = mid - 1;
	}
	printf("%d\n", res);
	return 0;
}