#include <bits/stdc++.h>
using namespace std;
#define pb push_back
#define eb emplace_back
#define bit(a) (1 << a)
#define lowbit(a) (a & (-a))
#define SZ(x) ((int)(x).size())
#define all(x) (x).begin(), (x).end()
#define debug(a) cout << #a << ":" << a << endl
typedef long long ll;
typedef vector<int> vi;
typedef pair<int, int> pii;
typedef vector<long long> vll;
typedef unsigned long long ull;
typedef vector<vector<int>> vvi;
typedef vector<array<int, 2>> va2;
constexpr int N = 1000010;
constexpr int INF = 2e9;
constexpr ll LLF = 2e18;
constexpr ll mod = 998244353;
constexpr int dir[4][2] = {{-1, 0}, {1, 0}, {0, -1}, {0, 1}};
ll powmod(ll a,ll b,ll mod=mod) {ll res=1;a%=mod;for(;b;b>>=1){if(b&1)res=res*a%mod;a=a*a%mod;}return res;}
ll inv(ll a){return powmod(a,mod-2);}
void solve() {
	ll n; cin >> n;
	vector<ll> a(n + 1);
	ll k = 1500;
	int ans = -1;
	for (int i = 1; i <= n; i++) {
		cin >> a[i];
		k += a[i];	
		if (k >= 4000 && ans == -1) {
			ans = i;
		}
	}	
	cout << ans;
}
int main() {
	ios::sync_with_stdio(false); cin.tie(nullptr);
	// cout << fixed << setprecision(10);
	// int testcase; cin >> testcase; for (int _ = 1; _ <= testcase; _++)
	solve();
	return 0;	
}