1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
#pragma GCC optimize ("Ofast")
#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
#define FOR(i, a, b) for (int i=(a); i<(b); i++)
#define FORD(i, a, b) for (int i=(a); i>(b); i--)
#define PPC(x) __builtin_popcount(x)
#define MSB(x) (63 - __builtin_clzll(x))
#define SZ(x) ((int)(x).size())
#define HASK(S, x) (S.find(x) != S.end())
#define pb push_back
#define ALL(x) (x).begin(), (x).end()
#define ithBit(m, i) ((m) >> (i) & 1)
#define ft first
#define sd second
#define kw(a) ((a) * (a))
#ifdef DEBUG
#include "debug.h"
#else
#define dbg(...) 0
#endif
using namespace std; 

template <typename T1, typename T2> inline void remin(T1& a, T2 b) { a = min(a, (T1)b);	}

const int maxN = 1 << 19, maxTS = maxN * 2;
const long long INF = 30000000000000000ll;

template <typename Tp> struct Tree_t
{
	int offset, qbegin, qend;
	Tp T[maxTS], res;
	
	void qpriv(int v, int left, int right)
	{	
		if (left >= qend or right <= qbegin)
			return;
		if (left >= qbegin and right <= qend)
		{
			remin(res, T[v]);
			return;
		}
		qpriv(v * 2, left, (left + right) / 2);
		qpriv(v*2+1, (left + right) / 2, right);
	}	
	
	void init(int n)
	{
		for (offset = 1; offset < n; offset *= 2) ;
		fill(T+1, T+offset*2, INF);
	}
	
	void updt(int v, long long x)
	{
		for (v += offset; v != 0; v /= 2)
			remin(T[v], x);
	}
	
	Tp query(int a, int b)
	{
		qbegin = a + offset;
		qend = b + offset;
		res = INF;
		qpriv(1, offset, offset * 2);
		return res;
	}
};
typedef Tree_t <long long> Tree;
Tree tree;

long long pref[maxN], dp[maxN];
vector <int> inds;

bool cmp(int i, int j)
{
	if (pref[i] == pref[j])
		return i < j;
	else
		return pref[i] < pref[j];
}

void solve()
{
	int n;
	scanf ("%d", &n);
	FOR(i, 1, n+1)
		scanf ("%lld", pref+i), pref[i] += pref[i-1];
	inds.resize(n+1);
	iota(ALL(inds), 0);
	sort(ALL(inds), cmp);
	tree.init(n+7);
	
	for (int i : inds)
	{
		dp[i] = tree.query(0, i) + i-1;
		if (i == 0)
			dp[i] = 0;
		tree.updt(i, dp[i]-i);
	}
	
	if (dp[n] > n)
		dp[n] = -1ll;
	printf("%lld\n", dp[n]);
}
 
int main()
{
	int t = 1;
	//scanf ("%d", &t);
	FOR(tid, 1, t+1)
	{
		//printf("Case #%d: ", tid);
		solve();
	}
	return 0;
}