#include <bits/stdc++.h>
using namespace std;
template <typename T>
using PQ = priority_queue<T>;
template <typename T>
using GPQ = priority_queue<T, vector<T>, greater<T>>;
using ll = long long;
template <class T>
ostream& operator<<(ostream& os, vector<T> v) {
  os << "[";
  for (auto vv : v) os << vv << ",";
  return os << "]";
}
template <class T>
ostream& operator<<(ostream& os, set<T> v) {
  os << "[";
  for (auto vv : v) os << vv << ",";
  return os << "]";
}
template <class L, class R>
ostream& operator<<(ostream& os, pair<L, R> p) {
  return os << "(" << p.first << "," << p.second << ")";
}
template <typename T>
T sq(T a) {
  return a * a;
}
template <typename T>
T gcd(T a, T b) {
  if (a > b) return gcd(b, a);
  return a == 0 ? b : gcd(b % a, a);
}
template <typename T, typename U>
T mypow(T b, U n) {
  if (n == 0) return 1;
  if (n == 1) return b;
  if (n % 2 == 0) {
    return mypow(b * b, n / 2);
  } else {
    return mypow(b, n - 1) * b;
  }
}
ll pcnt(ll b) { return __builtin_popcountll(b); }
vector<int> path[100010];
bool used[100010];
int cnt;
int dfs(int v) {
  int sum = 1;
  used[v] = true;
  for (int sv : path[v]) {
    if (used[sv]) continue;
    sum += dfs(sv);
  }
  sum %= 2;
  cnt += sum;
  return sum;
}
int main() {
  int N, M;
  cin >> N >> M;
  if (M != N - 1) terminate();
  for (int i = 0; i < M; ++i) {
    int a, b;
    cin >> a >> b;
    --a, --b;
    path[a].push_back(b);
    path[b].push_back(a);
  }
  fill(used, used + N, false);
  cnt = 0;
  cout << (dfs(0) == 0 ? cnt : -1) << endl;
  return 0;
}
