// Slower C++ solution:
#include<bits/stdc++.h>

using namespace std;

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

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

#define pb(x) push_back((x))

typedef long long ll;

inline int read(){

    register int x=0,f=1;register char ch=getchar();

    while(!isdigit(ch)){if(ch=='-')f=0;ch=getchar();}

    while(isdigit(ch)){x=x*10+(ch^'0');ch=getchar();}

    return f?x:-x;

}



const int N=1e5+5;

int n,m,dep[N],s,t,flg,S[N],k[N],stk[N],tp;

ll ans;

vector<int> E[N];



inline void Dfs(int u,int pa){

    for(int v:E[u]){

	if(v==pa)continue;

	if(dep[v]){flg=(dep[u]==dep[v]);s=u,t=v;continue;}

	dep[v]=dep[u]*-1;Dfs(v,u);

    }

}

inline void Cal(int u,int pa){

    for(int v:E[u]){

	if(v==pa||(u==s&&v==t)||(v==s&&u==t))continue;

	Cal(v,u);

	S[u]+=S[v];k[u]+=k[v];

    }

}



int main(){

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

    n=read(),m=read();

    REP(i,1,m){int u=read(),v=read();E[u].pb(v),E[v].pb(u);}

    dep[1]=1;Dfs(1,0);

    int sum=0;

    REP(i,1,n)sum+=(S[i]=dep[i]);

    if(m==n-1){if(sum)return puts("-1"),0;}

    else if((flg&&(sum&1))||(!flg&&sum))return puts("-1"),0;

    if(m==n){

	if(flg){

	    S[s]-=sum/2,S[t]-=sum/2;

	    ans+=abs(sum/2);

	}

	else k[s]=1,k[t]=-1;

    }

    Cal(1,0);

    REP(i,1,n)

	if(!k[i])ans+=abs(S[i]);

	else if(~k[i])stk[++tp]=-S[i];

	else stk[++tp]=S[i];

    stk[++tp]=0;

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

    int x=stk[(tp+1)>>1];

    REP(i,1,tp)ans+=abs(stk[i]-x);

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

    return 0;

}


// Faster C++ solution for the same problem (measured speedup: 1.353887289842892x):
#include <bits/stdc++.h>

#define int long long

using namespace std;



int n,m,head[100005],nxt[200005],pnt[200005],E = 0,sz[100005],s,t,ans = 0,k[100005];

bool odd = 0;

std::vector<int> v;



void add_edge(int u,int v)

{

	pnt[E] = v;

	nxt[E] = head[u];

	head[u] = E++;

}



void dfs1(int u,int fa)

{

	for (int i = head[u]; i != -1; i = nxt[i])

	{

		int v = pnt[i];

		if (v == fa) continue;

		if (sz[v])

		{

			if (sz[v] == sz[u]) odd = 1;

			s = u;

			t = v;

		}

		else

		{

			sz[v] = -sz[u];

			dfs1(v,u);

		}

	}

}



void dfs2(int u,int fa)

{

	for (int i = head[u]; i != -1; i = nxt[i])

	{

		int v = pnt[i];

		if (v == fa) continue;

		if (v == s && u == t) continue;

		if (v == t && u == s) continue;

		dfs2(v,u);

		sz[u] += sz[v];

		k[u] += k[v];

	}

}



signed main()

{

	memset(head,-1,sizeof(head));

	memset(sz,0,sizeof(sz));

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

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

	{

		int u,v;

		scanf("%lld%lld",&u,&v);

		add_edge(u,v);

		add_edge(v,u);

	}

	sz[1] = 1;

	dfs1(1,0);

	int sum = 0;

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

	{

		sum += sz[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);

			sz[s] -= sum >> 1;

			sz[t] -= sum >> 1;

		}

		else

		{

			if (sum)

			{

				puts("-1");

				return 0;

			}

			k[s] = 1;

			k[t] = -1;

		}

	}

	dfs2(1,0);

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

	{

		if (k[i]) v.push_back(k[i] * sz[i]);

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

	}

	v.push_back(0);

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

	int len = v.size();

	int mid = v[(len + 1) >> 1];

	for (int i = 0; i < len; i++)

	{

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

	}

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

	return 0;

}