// Slower C++ solution:
#define _CRT_SECURE_NO_WARNINGS

#include <iostream>

#include <sstream>

#include <iomanip>

#include <cstdio>

#include <cstdlib>

#include <cmath>

#include <cctype>

#include <cstring>

#include <vector>

#include <list>

#include <queue>

#include <deque>

#include <stack>

#include <map>

#include <set>

#include <algorithm>

#include <iterator>

#include <bitset>

#include <ctime>

#include<unordered_set>

#include<complex>

using namespace std;



#define FOR(i,a,b) for (int i = (a); i < (b); i++)

#define RFOR(i,b,a) for (int i = (b)-1; i >= (a); i--)

#define ITER(it,a) for (__typeof(a.begin()) it = a.begin(); it != a.end(); it++)

#define FILL(a,value) memset(a, value, sizeof(a))



#define SZ(a) (int)a.size()

#define ALL(a) a.begin(), a.end()

#define PB push_back

#define MP make_pair



typedef long long LL;

typedef vector<int> VI;

typedef pair<int, int> PII;



const double PI = acos(-1.0);

const int INF = 1000 * 1000 * 1000 + 7;

const LL LINF = INF * (LL)INF;



const int MAX = 1000 * 100 + 47;



vector<int> g[MAX];

int C[MAX];

int a = -1;

int b = -1;

bool isLoop;

bool odd;

int VAL[MAX];

int n, m;



void dfs(int v, int c, int p)

{

	C[v] = c;

	FOR(i, 0, SZ(g[v]))

	{

		int to = g[v][i];

		if (to == p) continue;

		if (C[to] != -1)

		{

			if (a == -1)

			{

				isLoop = true;

				if (C[to] != c ^ 1) odd = true;

				a = v;

				b = to;

			}



			continue;

		}



		dfs(to, c ^ 1, v);

	}

}



void imp()

{

	cout << -1 << endl;

	exit(0);

}



void rem(int a, int b)

{

	int ind = -1;

	FOR(i, 0, SZ(g[a]))

	{

		if (g[a][i] == b)

		{

			ind = i;

			break;

		}

	}



	g[a].erase(g[a].begin() + ind);

}



LL ans = 0;

LL dfs1(int v, int p)

{

	LL bal = VAL[v];

	FOR(i, 0, SZ(g[v]))

	{

		int to = g[v][i];

		if (to != p)

		{

			bal += dfs1(to, v);

		}

	}

	

	ans += abs(bal);

	return bal;

}



LL f(int c)

{

	ans = 0;

	VAL[a] += c;

	VAL[b] -= c;

	dfs1(0, 0);

	VAL[a] -= c;

	VAL[b] += c;

	return ans + abs(c);

}



int main()

{

	//freopen("in.txt", "r", stdin);

	//freopen("out.txt", "w", stdout);

	ios::sync_with_stdio(false); cin.tie(0);



	cin >> n >> m;

	FOR(i, 0, m)

	{

		int a, b;

		cin >> a >> b;

		a--;

		b--;

		g[a].push_back(b);

		g[b].push_back(a);

	}



	if (n % 2) imp();

	FILL(C, -1);

	dfs(0, 0, 0);

	int cnt = 0;

	FOR(i, 0, n)

	{

		cnt += C[i];

		VAL[i] = C[i] == 0 ? -1 : 1;

	}



	if (!isLoop)

	{

		if (cnt * 2 != n) imp();

		ans = 0;

		dfs1(0, 0);

		cout << ans << endl;

		return 0;

	}



	rem(a, b);

	rem(b, a);



	if (odd)

	{

		int val = (n - 2 * cnt) / 2;

		VAL[a] += val;

		VAL[b] += val;

		ans = 0;

		dfs1(0, 0);

		cout << ans + abs(val) << endl;

		return 0;

	}



	//FOR(i, 0, n)

	//{

	//	cout << VAL[i] << " ";

	//}

	

	//cout << endl;

	if (cnt * 2 != n) imp();

	int l = -n, r = n;

	while (r - l > 2)

	{

		int l1 = l + (r - l) / 3;

		int r1 = l + 2 * (r - l) / 3;

		if (f(l1) > f(r1))

		{

			l = l1;

		}

		else

		{

			r = r1;

		}

	}



	//cout << f(l) << " " << f(l + 1) << " " << f(l + 2) << endl;

	LL ans = min(f(l), min(f(l + 1), f(l + 2)));

	cout << ans << endl;

}

// Faster C++ solution for the same problem (measured speedup: 3.9166302034181357x):
#include <cmath>

#include <cstdio>

#include <cstring>

#include <iostream>

#include <algorithm>

using namespace std;

#define N 100005

#define ll long long

ll ans;

int n, m, S, T, A[N], siz[N];

int stk[N], top;

int tar[N << 1], nex[N << 1], fir[N], cnt;

bool odd;

void Add(int x, int y)

{

	++cnt;

	tar[cnt] = y;

	nex[cnt] = fir[x];

	fir[x] = cnt;

}

void Dfs1(int x, int fa)

{

	for (int i = fir[x]; i; i = nex[i])

	{

		int v = tar[i];

		if (v == fa)

			continue;

		if (siz[v])

		{

			if (siz[x] == siz[v])

				odd = 1;

			S = x, T = v;

		}

		else

		{

			siz[v] = -siz[x];

			Dfs1(v, x);

		}

	}

}

void Dfs2(int x, int fa)

{

	for (int i = fir[x]; i; i = nex[i])

	{

		int v = tar[i];

		if (v == fa || (x == S && v == T) || (x == T && v == S))

			continue;

		Dfs2(v, x);

		siz[x] += siz[v];

		A[x] += A[v];

	}

}

int main()

{

	scanf("%d%d", &n, &m);

	for (int i = 1; i <= m; i++)

	{

		int x, y;

		scanf("%d%d", &x, &y);

		Add(x, y), Add(y, x);

	}

	siz[1] = 1, Dfs1(1, 0);

	int sum = 0;

	for (int i = 1; i <= n; i++)

		sum += siz[i];

	if (m == n - 1)

	{

		if (sum)

		{

			puts("-1");

			return 0;

		}

	}

	else

	{

		if (odd)

		{

			if (sum & 1)

			{

				puts("-1");

				return 0;

			}

			ans += abs(sum>>1);

			siz[S] -= sum >> 1;

			siz[T] -= sum >> 1;

		}

		else

		{

			if (sum)

			{

				puts("-1");

				return 0;

			}

			else

				A[S] = 1, A[T] = -1;

		}

	}

	Dfs2(1, 0);

	for (int i = 1; i <= n; i++)

	{

		if (A[i])

			stk[++top] = A[i] * siz[i];

		else

			ans += abs(siz[i]);

	}

	stk[++top] = 0;

	sort(stk + 1, stk + top + 1);

	int mid = stk[(top + 1) >> 1];

	for (int i = 1; i <= top; i++)

		ans += abs(stk[i] - mid);

	printf("%lld\n", ans);

}