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#include <bits/stdc++.h>

using namespace std;

constexpr int MAXN = 500000;

typedef long long ll;
int n;
ll a[MAXN + 1];

int s[MAXN + 1];
int p[MAXN + 1];

void LongestSeq() {
	int len = 1;
	s[0] = 0;

        for (int i = 0; i <= n; i++) {
           if (a[i] < 0) continue;
           int l = 0;
           int r = len;
           // a[s[l]] <= a[i] < a[s[r]]
           while (l + 1 < r) {
                int m = (l + r) / 2;
                if (a[s[m]] <= a[i]) l = m;
                else r = m;
           }
           p[i] = s[l];
           s[r] = i;
           len = max(len, r + 1);
	}
}

int Cost() {
   int cost = 0;
   for (int i = n; i > 0; i = p[i]) cost += i - p[i] - 1;
   return cost;
}

int main() {
   scanf("%d", &n);
   a[0] = 0;
   for (int i = 1; i <= n; i++) {
       int ai;
       scanf("%d", &ai);
       a[i] = a[i - 1] + ai;
   }
   if (a[n] < 0) {
       printf("-1\n");
       return 0;
    }
    LongestSeq();
    printf("%d\n", Cost());
    return 0;
}