#include <bits/stdc++.h>

using namespace std;

const int MAXN = 100100;
const int INF = 1<<30;

int arr[MAXN];
int dp[MAXN][2];

int main()
{
	freopen("negsort.in", "r", stdin);
	freopen("negsort.out", "w", stdout);
	
	int n, i, x;
	
	cin>>n;
	
	for (i = 0; i < n; ++i)
		cin>>arr[i];
	
	dp[n - 1][0] = dp[n - 1][1] = 0;
	for (i = n - 2; i >= 0; --i) for (x = 0; x <= 1; ++x)
	{
		dp[i][x] = INF;
		if (arr[i + 1] >= (1 - 2 * x) * arr[i])
			dp[i][x] = min(dp[i][x], dp[i + 1][0]);
		if (-arr[i + 1] >= (1 - 2 * x) * arr[i])
			dp[i][x] = min(dp[i][x], 1 + dp[i + 1][1]);
	}
	
	x = min(dp[0][0], 1 + dp[0][1]);
	cout<<(x == INF ? -1 : x)<<'\n';
}