#include<bits/stdc++.h>
#define sqr(x) ((x)*(x))
#define ll long long
#define ull unsigned long long
#define ui unsigned int
#define ld long double
#define vi vector<int>
#define HEAP(...) priority_queue<__VA_ARGS__ >
#define heap(...) priority_queue<__VA_ARGS__,vector<__VA_ARGS__ >,greater<__VA_ARGS__ > > 
#define pii pair<int,int> 
#define pb push_back
#define mp make_pair
#define debuge cerr<<"isok"<<endl
#define debug(x) cerr<<#x<<"="<<x<<endl
#define dprintf(...) fprintf(stderr,__VA_ARGS__)
#define SS second
#define FF first
#define ls (k<<1)
#define rs (k<<1|1)
#define clr(a,x) memset(a,x,sizeof(a))
#define cpy(a,x) memcpy(a,x,sizeof(a))
#define file(x) freopen(x".in","r",stdin),freopen(x".out","w",stdout)
#define SZ(x) ((int)x.size())
using namespace std;
template<class T> inline void gmin(T &x,const T &y){if(x>y) x=y;}
template<class T> inline void gmax(T &x,const T &y){if(x<y) x=y;}
const int BufferSize=1<<16;
char buffer[BufferSize],*Bufferhead,*Buffertail;
bool Terminal;
inline char Getchar(){
	if(Bufferhead==Buffertail){
		int l=fread(buffer,1,BufferSize,stdin);
		if(!l){Terminal=1;return 0;}
		Buffertail=(Bufferhead=buffer)+l;
	}
	return *Bufferhead++;
}
template<class T>inline bool read(T &x){
	x=0;char c=Getchar(),rev=0;
	while(c<'0'||c>'9'){rev|=c=='-';c=Getchar();if(Terminal)return 0;}
	while(c>='0'&&c<='9') x=x*10+c-'0',c=Getchar();
	if(c=='.'){
		c=Getchar();double t=0.1;
		while(c>='0'&&c<='9') x=x+(c-'0')*t,c=Getchar(),t=t/10;
	}
	x=rev?-x:x;
	return 1;
}
template<class T1,class T2> inline bool read(T1 &x,T2 &y){return read(x)&read(y);}
template<class T1,class T2,class T3> inline bool read(T1 &x,T2 &y,T3 &z){return read(x)&read(y)&read(z);}
template<class T1,class T2,class T3,class T4> inline bool read(T1 &x,T2 &y,T3 &z,T4 &w){return read(x)&read(y)&read(z)&read(w);}
inline bool reads(char *x){
	char c=Getchar();
	while(c<33||c>126){c=Getchar();if(Terminal)return 0;}
	while(c>=33&&c<=126) (*x++)=c,c=Getchar();
	*x=0;return 1;
}
template<class T>inline void print(T x,const char c='\n'){
	if(!x){putchar('0');putchar(c);return;}
	if(x<0) putchar('-'),x=-x;
	int m=0,a[20];
	while(x) a[m++]=x%10,x/=10;
	while(m--) putchar(a[m]+'0');
	putchar(c);
}
//--------------------------------head---------------------------------------------

const int inf=0x3f3f3f3f;
const int N=200005,M=100005,mod=1e9+7;
template<class T,class S> inline void ch(T &x,const S y){x=(x+y)%mod;}
inline int exp(int x,int y,const int mod=::mod){
	int ans=1;
	while(y){
		if(y&1) ans=(ll)ans*x%mod;
		x=(ll)x*x%mod;y>>=1;
	}return ans;
}

int n,m,dep[N],fa[N],x[N];
ll ans,k[N],b[N];
bool vis[N];
vi g[N],cir;

inline int dfs(int x){
	int use=0;
	vis[x]=1;
	for(int y:g[x])
		if(!vis[y]) use+=dfs(y);
	ans+=abs(1-use);
	return 1-use;
}
void predfs(int x){
	vis[x]=1;
	for(int y:g[x]){
		if(vis[y]){
			if(dep[y]>dep[x]){
				cir.pb(y);
				while(y!=x)
					y=fa[y],cir.pb(y);
			}
			continue;
		}
		dep[y]=dep[x]+1;fa[y]=x;
		predfs(y);
	}
}

int main(){
#ifdef rqgao2014
	freopen("input.txt","r",stdin);
#endif
	scanf("%d%d",&n,&m);
	for(int i=1;i<=m;i++){
		int x,y;scanf("%d%d",&x,&y);
		g[x].pb(y);g[y].pb(x);
	}
	if(m==n-1){
		if(dfs(1)){puts("-1");return 0;}
		printf("%lld\n",ans);
		return 0;
	}
	predfs(1);n=0;
	clr(vis,0);
	for(int i:cir) vis[i]=1;
	for(int i:cir){
		x[++n]=dfs(i);
		ans-=abs(x[n]);
	}
	k[1]=1;b[1]=0;
	for(int i=1;i<n;i++)
		k[i+1]=-k[i],b[i+1]=x[i]-b[i];
	if(n&1){
		ll X=x[n]-b[1]-b[n];
		if(X&1){puts("-1");return 0;}
		X/=2;
		for(int i=1;i<=n;i++)
			ans+=abs(k[i]*X+b[i]);
		printf("%lld\n",ans);
	}
	else{
		if(b[1]+b[n]!=x[n]){puts("-1");return 0;}
		for(int i=2;i<=n;i+=2) b[i]=-b[i];
		sort(b+1,b+n+1);
		for(int i=1;i<=n;i++)
			ans+=abs(b[n/2]-b[i]);
		printf("%lld\n",ans);
	}
	return 0;
}

Measured memory_bytes: 20344