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 <bits/stdc++.h>
using namespace std;
namespace my_header {
const int INF = 0x3f3f3f3f;
inline char gchar() {
  char ret = getchar();
  for (; ret == '\n' || ret == '\r' || ret == ' '; ret = getchar())
    ;
  return ret;
}
template <class T>
inline void fr(T &ret, char c = ' ', int flg = 1) {
  for (c = getchar(); (c < '0' || '9' < c) && c != '-'; c = getchar())
    ;
  if (c == '-') {
    flg = -1;
    c = getchar();
  }
  for (ret = 0; '0' <= c && c <= '9'; c = getchar()) ret = ret * 10 + c - '0';
  ret = ret * flg;
}
inline int fr() {
  int t;
  fr(t);
  return t;
}
template <class T>
inline void fr(T &a, T &b) {
  fr(a), fr(b);
}
template <class T>
inline void fr(T &a, T &b, T &c) {
  fr(a), fr(b), fr(c);
}
template <class T>
inline char wr(T a, int b = 10, bool p = 1) {
  return a < 0 ? putchar('-'), wr(-a, b, 0)
               : (a == 0 ? (p ? putchar('0') : p)
                         : (wr(a / b, b, 0), putchar('0' + a % b)));
}
template <class T>
inline T gcd(T a, T b) {
  return b == 0 ? a : gcd(b, a % b);
}
template <class T>
inline T fpw(T b, T i, T _m, T r = 1) {
  for (; i; i >>= 1, b = b * b % _m)
    if (i & 1) r = r * b % _m;
  return r;
}
};  // namespace my_header
using namespace my_header;
int n, d, t[22222], c, ans;
priority_queue<pair<int, int>, vector<pair<int, int> >,
               greater<pair<int, int> > >
    q;
int main() {
  fr(n, d);
  for (int i = 0; i < n; ++i) t[i] = fr() < 0, c += t[i];
  t[n] = 1;
  if (c > d) {
    puts("-1");
  } else {
    int l = -1;
    for (int i = 0; i < n; ++i) {
      if (t[i + 1] == 1 && t[i] == 0 && l != -1)
        q.push(make_pair(i - l, i == n - 1));
      if (t[i]) l = i;
    }
    d -= c;
    ans = q.size() * 2;
    if (ans == 2) {
      printf("1\n");
      return 0;
    }
    while (!q.empty()) {
      pair<int, int> t = q.top();
      q.pop();
      if (t.first <= d) {
        d -= t.first;
        ans -= 2;
        ans += t.second;
      } else
        break;
    }
    wr(ans), puts("");
  }
  return 0;
}
