#include <bits/stdc++.h>
using namespace std;
using lint = long long int;
using pint = pair<int, int>;
using plint = pair<lint, lint>;
struct fast_ios { fast_ios(){ cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_;
#define FOR(i, begin, end) for(int i=(begin),i##_end_=(end);i<i##_end_;i++)
#define IFOR(i, begin, end) for(int i=(end)-1,i##_begin_=(begin);i>=i##_begin_;i--)
#define REP(i, n) FOR(i,0,n)
#define IREP(i, n) IFOR(i,0,n)
template<typename T> istream &operator>>(istream &is, vector<T> &vec){ for (auto &v : vec) is >> v; return is; }
template<typename T> ostream &operator<<(ostream &os, const vector<T> &vec){ os << "["; for (auto v : vec) os << v << ","; os << "]"; return os; }
template<typename T> ostream &operator<<(ostream &os, const deque<T> &vec){ os << "deq["; for (auto v : vec) os << v << ","; os << "]"; return os; }
template<typename T> ostream &operator<<(ostream &os, const set<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream &operator<<(ostream &os, const unordered_set<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream &operator<<(ostream &os, const multiset<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream &operator<<(ostream &os, const unordered_multiset<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &pa){ os << "(" << pa.first << "," << pa.second << ")"; return os; }
template<typename TK, typename TV> ostream &operator<<(ostream &os, const map<TK, TV> &mp){ os << "{"; for (auto v : mp) os << v.first << "=>" << v.second << ","; os << "}"; return os; }
template<typename TK, typename TV> ostream &operator<<(ostream &os, const unordered_map<TK, TV> &mp){ os << "{"; for (auto v : mp) os << v.first << "=>" << v.second << ","; os << "}"; return os; }
template<typename T> void ndarray(vector<T> &vec, int len) { vec.resize(len); }
template<typename T, typename... Args> void ndarray(vector<T> &vec, int len, Args... args) { vec.resize(len); for (auto &v : vec) ndarray(v, args...); }
template<typename T> void Max(T &m, const T q) { if (m < q) m = q; }
template<typename T> void Min(T &m, const T q) { if (m > q) m = q; }
template<typename T1, typename T2> pair<T1, T2> operator+(pair<T1, T2> &l, pair<T1, T2> &r) { return make_pair(l.first + r.first, l.second + r.second); }
template<typename T1, typename T2> pair<T1, T2> operator-(pair<T1, T2> &l, pair<T1, T2> &r) { return make_pair(l.first - r.first, l.second - r.second); }
#define dbg(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ") " << __FILE__ << endl;

int N, M;
vector<set<int>> to;
vector<lint> score;
int main()
{
    cin >> N >> M;
    to.resize(N);
    REP(_, M)
    {
        int a, b;
        cin >> a >> b;
        a--;
        b--;
        to[a].insert(b);
        to[b].insert(a);
    }

    queue<int> haji;
    REP(i, N) if (to[i].size() == 1) haji.push(i);

    score.resize(N, 1);
    set<int> nokori;
    REP(i, N) nokori.insert(i);

    lint res = 0;
    while (!haji.empty())
    {
        int now = haji.front();
        haji.pop();
        if (to[now].empty()) continue;
        int nxt = *to[now].begin();
        res += abs(score[now]);
        score[nxt] -= score[now];
        to[now].clear();
        nokori.erase(now);
        to[nxt].erase(now);
        if (to[nxt].size() == 1) haji.push(nxt);
    }

    if (nokori.size() == 1)
    {
        // 木の場合
        cout << (score[*nokori.begin()] == 0 ? res : -1) << endl;
        return 0;
    }
    else
    {
        vector<lint> yy;
        int now = *nokori.begin();
        while (to[now].size() >= 1)
        {
            int nxt = *to[now].begin();
            to[now].erase(nxt);
            to[nxt].erase(now);
            yy.push_back(score[nxt]);
            now = nxt;
        }

        if (nokori.size() % 2 == 1)
        {
            // 奇数ループが残った場合
            lint su = accumulate(yy.begin(), yy.end(), 0LL);
            if (abs(su % 2) == 1)
            {
                cout << -1 << endl;
                return 0;
            }
            else su /= 2;
            for (int i = 1; i < yy.size(); i += 2) su -= yy[i];
            REP(i, yy.size())
            {
                res += abs(su);
                su = yy[i] - su;
            }
            cout << res << endl;
        }
        else
        {
            // 偶数ループが残った場合
            vector<lint> su(2);
            REP(i, yy.size()) su[i % 2] += yy[i];
            if (su[0] != su[1])
            {
                cout << -1 << endl;
                return 0;
            }
            else
            {
                vector<lint> v;
                lint n = 0;
                REP(i, yy.size())
                {
                    v.push_back(n * (i % 2 == 0 ? 1 : -1));
                    n = yy[i] - n;
                }

                sort(v.begin(), v.end());
                REP(i, v.size()) res += abs(v[i] - v[v.size() / 2]);
                cout << res << endl;
            }
        }
    }
}


Measured memory_bytes: 20988