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#include <bits/stdc++.h>
#define IOSTREAM_BOOST true
using namespace std;

int n;
int tab[500005];
int prefsum[500005];

set<pair<long long, int>> vals;
long long valm = 0;

int dp[500005];
int dpm = 0;

int getDp(int x){
    return (x >= 0 ? dp[x] : 0);
}

int main()
{
    #if IOSTREAM_BOOST
    ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
    #endif
    
    cin >> n;
    for(int i = 0; i < n; i++) cin >> tab[i], prefsum[i + 1] = prefsum[i] + tab[i]; 

    for(int i = 0; i < n; i++){
        valm += tab[i];

        pair<int, int> elem = {tab[i] - valm, getDp(i - 1) - dpm};
        while(true){
            auto ait = vals.lower_bound(elem);
            if(ait == vals.begin()) break;
            ait--;
            if(ait->second + dpm >= elem.second + dpm) vals.erase(ait); 
            else break;
        }
        vals.insert(elem);

        auto it = vals.lower_bound({-valm, -1e9});

        if(it != vals.end()) dp[i] = it->second + dpm;
        else dp[i] = 1e9;
        dpm++;
    }
    cout << (dp[n - 1] >= 1e9 ? -1 : dp[n - 1]) << "\n";

    //for(int i = 0; i < n; i++) cout << dp[i] << " ";
    return 0;
}