// Slower C++ solution:
#include <iostream>

#include <cstdio>

#include <map>

#include <set>

#include <vector>

#include <algorithm>

#include <cstdlib>

#include <queue>

#include <cmath>

#include <cstring>

using namespace std;



void init();

void solve();

int main(){

try { 



#ifndef CUSTOM_MAIN

#ifdef MULTIPLE_TEST_CASES_WITH_T



int T; scanf("%d",&T); while(T--) {init(); solve();}



#else

#ifdef MULTIPLE_TEST_CASES_WITHOUT_T



while(1) {try{init(); } catch(bool t){return 0;} solve(); }



#else



init(); solve();



#endif

#endif

#endif



} catch (const char* s) { return 0; }

    return 0;

}



#ifdef ENABLE_LL

#define int long long

#endif



#ifdef ENABLE_LL

#define I "%lld"

#define II "%lld%lld"

#define III "%lld%lld%lld"

#define IIII "%lld%lld%lld%lld"

#define IN "%lld\n"

#define IIN "%lld%lld\n"

#define IIIN "%lld%lld%lld\n"

#define IIIIN "%lld%lld%lld%lld\n"

#else

#define I "%d"

#define II "%d%d"

#define III "%d%d%d"

#define IIII "%d%d%d%d"

#define IN "%d\n"

#define IIN "%d%d\n"

#define IIIN "%d%d%d\n"

#define IIIIN "%d%d%d%d\n"

#endif



#ifdef __LOCALE__

#define see(a) std::cout << #a << "=" << a << std::endl

#define ses(a) std::cout << #a << "=" << a << " " 

#else

#define see(a) //std::cout << #a << "=" << a << std::endl

#define ses(a)

#endif

#define repe(a,b) for (int a=0;a<(int)b.size();a++)

#define rep(i,n) for (int i=0;i<n;i++)

#define repa(i,n) for (int i=1;i<=n;i++)

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

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

typedef pair < int , int > pr; typedef pair < pr  , int > prr;

#define L first

#define R second

template <class T> inline bool checkMin(T& a , T b) { return (a > b ? a=b,1 : 0); }

template <class T> inline bool checkMax(T& a , T b) { return (a < b ? a=b,1 : 0); }

class Scanner{ private: istream& ist;public: Scanner(istream& in):ist(in){} string next(){ string r; ist >> r; return r; } string nextLine(){ string r; getline(ist,r); return r; } int nextInt(){ int r; ist >> r; return r; } double nextDouble(){ double r; ist >> r; return r; } char nextChar(){ char r; ist>>r; return r;} }; Scanner sc(cin);

void ALERT(bool judgememt, const char* phrase) { if (judgememt) { puts(phrase); throw "ALERT"; } }

bool alert(bool judgememt, const char* phrase) { if (judgememt) puts(phrase); return judgememt; }



const int N = 100005;

vector <int> e[N]; int n, m;

int sz[N], k[N];



void init() {

    scanf(II,&n,&m);

    rep (i,m) {

        int u, v; scanf(II,&u,&v);

        e[u].push_back(v); e[v].push_back(u); }

}



int S, T;

void dfs1(int u, int f) {

    sz[u]=-sz[f];

    for (int v: e[u]) {

        if (v==f) continue;

        if (sz[v]!=0) { S=u; T=v; }

        else dfs1(v,u); } }

void dfs2(int u, int f) {

    ses(u);see(f);

    for (int v:e[u]) {

        if (v==f || (S==v&&T==u) || (S==u&&T==v)) continue;

        dfs2(v,u); k[u]+=k[v]; sz[u]+=sz[v]; } }



void solve() {

    sz[0]=-1; dfs1(1,0);

    int ans=0;



    // judge -1 verdict

    int sum=0; repa (i,n) sum+=sz[i];

    if (m==n-1) { ALERT(sum!=0,"-1"); }

    else {

        if (sz[S]==sz[T]) { // odd circle

            ALERT(sum&1, "-1");

            ans += abs(sum/2); sz[S]-=sum/2; sz[T]-=sum/2; }

        else { //even circle

            ALERT(sum!=0, "-1");

            k[S]=1; k[T]=-1; /* set k in the path from S to T  */ } }

    dfs2(1,0);

    vector <int> st; st.push_back(0);

    repa (i,n) {

        if (k[i]!=0) st.push_back(k[i]*sz[i]); 

        else ans+=abs(sz[i]); }

    sort(st.begin(),st.end()); 

    int m=st[st.size()/2];

    for (int i: st) ans+= abs(i-m);

    printf(IN,ans);

}




// Faster C++ solution for the same problem (measured speedup: 2.560876958660684x):
#include <bits/stdc++.h>

using namespace std;

const int N = 1e5 + 9, M = 2 * N;

int h[N], w[M],o, q[M], f[N], c[N], v[N];

int get(int y)

{

    if(y==f[y]) return y ; 

    return f[y]=get(f[y]);

}

void dfs(int n, int m)

{

    c[n] = m;

    for (int i = h[n]; i; i = w[i])

        if (q[i]!= f[n])

        {

            f[q[i]] = n;

            dfs(q[i], -m);

            c[n] += c[q[i]];

        }

}

int a, b, qq = 1, ww = 1, ans = 0;

int qw , wq;

int main()

{

    for (int i = 1; i <= 100000; ++i)

    {

        f[i] = i;

    }

    cin>>a>>b;

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

    {

        cin>>qw>>wq;

        if (get(qw) != get(wq))

        {

            f[f[qw]] = f[wq];

        }

        else

        {

            qq = qw;

             ww = wq;

            continue;

        }

        o++;

        w[o] = h[qw];

        q[o] = wq;

        h[qw]=o;

        o++;

        w[o] = h[wq];

        q[o] = qw;

        h[wq]=o;

    }

    f[qq] = 0;

    dfs(qq, 1);

    if (a == b)

    {

        long long u=0;

        for (int i = ww; i; i = f[i])

        {

            u++;

            v[u] = c[i];

        }

        if (u % 2)

        {

            if (c[qq] % 2)

            {

                cout<<"-1";

                return 0;

            }

            for (int i = ww; i; i = f[i])

            {

                c[i] -= c[qq] / 2;

            }

        }

        else

        {

            if (c[qq])

            {

                cout<<"-1";

                return 0;

            }

            sort(v + 1, v + u + 1);

            for (int i = ww; i; i = f[i])

            {

                c[i] -= v[u / 2];

            }

        }

    }

    else if (c[qq])

    {

        cout<<"-1";

        return 0;

    }

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

    {

        ans += abs(c[i]);

    }

    cout<<ans;

    return 0;

}