100 1
1000000 100 1000
 5 3
1 4 10
2 2 5
3 1 6
 10 4
1 5 20
2 5 200
100 6 20
101 1 100
 5 3
1 3 4
4 3 4
6 4 1
 4 1
6 1 1
 8 6
1 3 20
4 2 1
6 6 5
9 1 1
15 3 6
21 8 8
 4 5
1 2 3
2 1 3
3 1 2
4 3 3
5 4 1
 8 4
1 3 2
2 3 100
10 6 20
11 5 20
 4 10
1 1 1
3 1 2
4 1 2
6 1 2
8 1 2
13 1 2
16 1 1
17 1 2
19 3 1
20 1 1
 5 3
1 4 4
4 2 2
5 5 2
 4 3
1 3 10
2 2 15
12 4 1
 5 4
1 1 4
2 4 4
5 2 20
11 5 2
 1 10
4 1 1
9 1 1
10 1 1
12 1 1
13 1 1
15 1 1
16 1 1
18 1 1
19 1 1
20 1 1

5050
 10
-1
5
 15
40
-1
1
 6
-1
10
 1
 6
9
-1
4
15
36
 3
3
4
-1
10
 6
15
-1
21
 1
1
2
1
1
1
1
1
6
1
 10
-1
15
 6
-1
10
 1
14
-1
15
 1
1
1
1
1
1
1
1
1
1

#include <stdio.h>
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

#define ll long long
#define ull unsigned long long
#define ld long double
#define rep(i, l, r) for (int i = l; i < r; i++)
#define sz(a) (int)a.size()
#define fi first
#define se second

using namespace std;
using namespace __gnu_pbds;

typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update> ordered_set;

const int N = 1000;
const int inf = (int)1e9 + 1;
const ll big = (ll)1e18 + 1;
const int MOD = (int)1e9 + 7;
const int MOD1 = (int)1e9 + 9;

void print(vector<int> &a)
{
    for (int i : a)
        cout << i << " ";
    cout << endl;
}

int main()
{
    //freopen("a.in", "r", stdin);
    //freopen("lasers.out", "w", stdout);
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int n, k;
    cin >> n >> k;
    int a[n];
    rep(i, 0, n)
        cin >> a[i];
    int l = -1;
    vector<pair<int, int> > b;
    int sum = 0;
    rep(i, 0, n)
    {
        if (a[i] < 0 && l == -1)
            l = i;
        if (l != -1 && (i == n - 1 || a[i + 1] >= 0))
        {
            sum += i - l + 1;
            b.push_back({l, i});
            l = -1;
        }
    }
    if (sum > k)
    {
        cout << -1;
        return 0;
    }
    if (sum == 0)
    {
        cout << 0;
        return 0;
    }
    k -= sum;
    int k1 = k;
    int ans = sz(b) * 2, ans1 = sz(b) * 2;
    vector<int> cnt;
    rep(i, 0, sz(b) - 1)
        cnt.push_back(b[i + 1].fi - b[i].se - 1);
    sort(cnt.begin(), cnt.end());
    rep(i, 0, sz(cnt))
        if (k >= cnt[i])
        {
            k -= cnt[i];
            ans -= 2;
        }
    if (k1 >= n - b[sz(b) - 1].se - 1)
    {
        k1 -= n - b[sz(b) - 1].se - 1;
        ans1--;
    }
    rep(i, 0, sz(cnt))
        if (k1 >= cnt[i])
        {
            k1 -= cnt[i];
            ans1 -= 2;
        }
    cout << min(ans, ans1) << endl;
    return 0;
}
