#include<bits/stdc++.h>

typedef unsigned int uint;
typedef long long ll;
typedef unsigned long long ull;
typedef double lf;
typedef long double llf;
typedef std::pair<int,int> pii;

#define xx first
#define yy second

template<typename T> inline T max(T a,T b){return a>b?a:b;}
template<typename T> inline T min(T a,T b){return a<b?a:b;}
template<typename T> inline T abs(T a){return a>0?a:-a;}
template<typename T> inline bool repr(T &a,T b){return a<b?a=b,1:0;}
template<typename T> inline bool repl(T &a,T b){return a>b?a=b,1:0;}
template<typename T> inline T gcd(T a,T b){T t;if(a<b){while(a){t=a;a=b%a;b=t;}return b;}else{while(b){t=b;b=a%b;a=t;}return a;}}
template<typename T> inline T sqr(T x){return x*x;}
#define mp(a,b) std::make_pair(a,b)
#define pb push_back
#define I inline
#define mset(a,b) memset(a,b,sizeof(a))
#define mcpy(a,b) memcpy(a,b,sizeof(a))

#define fo0(i,n) for(int i=0,i##end=n;i<i##end;i++)
#define fo1(i,n) for(int i=1,i##end=n;i<=i##end;i++)
#define fo(i,a,b) for(int i=a,i##end=b;i<=i##end;i++)
#define fd0(i,n) for(int i=(n)-1;~i;i--)
#define fd1(i,n) for(int i=n;i;i--)
#define fd(i,a,b) for(int i=a,i##end=b;i>=i##end;i--)
#define foe(i,x)for(__typeof(x.end())i=x.begin();i!=x.end();++i)

struct Cg{I char operator()(){return getchar();}};
struct Cp{I void operator()(char x){putchar(x);}};
#define OP operator
#define RT return *this;
#define RX x=0;char t=P();while((t<'0'||t>'9')&&t!='-')t=P();bool f=0;\
if(t=='-')t=P(),f=1;x=t-'0';for(t=P();t>='0'&&t<='9';t=P())x=x*10+t-'0'
#define RL if(t=='.'){lf u=0.1;for(t=P();t>='0'&&t<='9';t=P(),u*=0.1)x+=u*(t-'0');}if(f)x=-x
#define RU x=0;char t=P();while(t<'0'||t>'9')t=P();x=t-'0';for(t=P();t>='0'&&t<='9';t=P())x=x*10+t-'0'
#define TR *this,x;return x;
I bool IS(char x){return x==10||x==13||x==' ';}template<typename T>struct Fr{T P;I Fr&OP,(int&x)
{RX;if(f)x=-x;RT}I OP int(){int x;TR}I Fr&OP,(ll &x){RX;if(f)x=-x;RT}I OP ll(){ll x;TR}I Fr&OP,(char&x)
{for(x=P();IS(x);x=P());RT}I OP char(){char x;TR}I Fr&OP,(char*x){char t=P();for(;IS(t);t=P());if(~t){for(;!IS
(t)&&~t;t=P())*x++=t;}*x++=0;RT}I Fr&OP,(lf&x){RX;RL;RT}I OP lf(){lf x;TR}I Fr&OP,(llf&x){RX;RL;RT}I OP llf()
{llf x;TR}I Fr&OP,(uint&x){RU;RT}I OP uint(){uint x;TR}I Fr&OP,(ull&x){RU;RT}I OP ull(){ull x;TR}};Fr<Cg>in;
#define WI(S) if(x){if(x<0)P('-'),x=-x;char s[S],c=0;while(x)s[c++]=x%10+'0',x/=10;while(c--)P(s[c]);}else P('0')
#define WL if(y){lf t=0.5;for(int i=y;i--;)t*=0.1;if(x>=0)x+=t;else x-=t,P('-');*this,(ll)(abs(x));P('.');if(x<0)\
x=-x;while(y--){x*=10;x-=floor(x*0.1)*10;P(((int)x)%10+'0');}}else if(x>=0)*this,(ll)(x+0.5);else *this,(ll)(x-0.5);
#define WU(S) if(x){char s[S],c=0;while(x)s[c++]=x%10+'0',x/=10;while(c--)P(s[c]);}else P('0')
template<typename T>struct Fw{T P;I Fw&OP,(int x){WI(10);RT}I Fw&OP()(int x){WI(10);RT}I Fw&OP,(uint x){WU(10);RT}
I Fw&OP()(uint x){WU(10);RT}I Fw&OP,(ll x){WI(19);RT}I Fw&OP()(ll x){WI(19);RT}I Fw&OP,(ull x){WU(20);RT}I Fw&OP()
(ull x){WU(20);RT}I Fw&OP,(char x){P(x);RT}I Fw&OP()(char x){P(x);RT}I Fw&OP,(const char*x){while(*x)P(*x++);RT}
I Fw&OP()(const char*x){while(*x)P(*x++);RT}I Fw&OP()(lf x,int y){WL;RT}I Fw&OP()(llf x,int y){WL;RT}};Fw<Cp>out;

const int N=100007;

std::vector<int>p[N];
int n,m,ra,rb,fa[N],sa[N],sb[N],col[N],f[N];

inline int find(int x)
{
	return x==fa[x]?x:fa[x]=find(fa[x]);
}

inline void dfs(int x)
{
	sa[x]=col[x],sb[x]=!col[x];
	foe(i,p[x])if(*i!=fa[x])fa[*i]=x,col[*i]=!col[x],dfs(*i),sa[x]+=sa[*i],sb[x]+=sb[*i];
}

inline void dfs2(int x)
{
	sa[x]=col[x];
	foe(i,p[x])if(*i!=fa[x])dfs2(*i),sa[x]+=sa[*i];
}

inline int dep(int x)
{
	int t=0;
	for(;x;x=fa[x])t++;
	return t;
}

int main()
{
	in,n,m;
	fo1(i,n)fa[i]=i;
	fo1(i,m)
	{
		int x,y;
		in,x,y;
		if(find(x)==find(y))ra=x,rb=y;
		else fa[find(x)]=find(y),p[x].pb(y),p[y].pb(x);
	}
	fa[1]=0;
	dfs(1);
	if(m==n-1)
	{
		if(sa[1]!=sb[1])out,-1,'\n';
		else
		{
			int t=0;
			fo1(i,n)t+=abs(sa[i]-sb[i]);
			out,t,'\n';
		}
		return 0;
	}
	if(col[ra]==col[rb])
	{
		if((sa[1]^sb[1])&1)out,-1,'\n';
		else
		{
			int t=0,x=(sb[1]-sa[1])/2;
			col[ra]+=x,col[rb]+=x;
			dfs2(1);
			fo1(i,n)t+=abs(sa[i]-sb[i]);
			out,t+abs(x),'\n';
		}
		return 0;
	}
	if(sa[1]!=sb[1]){out,-1,'\n';return 0;}
	int x=ra,y=rb,a=dep(x),b=dep(y),c=0;
	if(a<b)std::swap(a,b),std::swap(x,y);
	if(a>b)fo0(i,a-b)f[c++]=sa[x]-sb[x],sa[x]=sb[x],x=fa[x];
	for(;x!=y;x=fa[x],y=fa[y])f[c++]=sa[x]-sb[x],f[c++]=sb[y]-sa[y],sa[x]=sb[x],sa[y]=sb[y];
	f[c++]=0;
	std::nth_element(f,f+c/2,f+c);
	int t=0;
	fo1(i,n)t+=abs(sa[i]-sb[i]);
	fo0(i,c)t+=abs(f[i]-f[c/2]);
	out,t,'\n';
}

Measured memory_bytes: 10496