#include<deque>
#include<queue>
#include<vector>
#include<algorithm>
#include<iostream>
#include<set>
#include<cmath>
#include<tuple>
#include<string>
#include<chrono>
#include<functional>
#include<iterator>
#include<random>
#include<unordered_set>
#include<unordered_map>
#include<array>
#include<map>
#include<bitset>
#include<iomanip>
#include<list>
#include <numeric>
using namespace std;
typedef unsigned long long int ulint;
typedef long long int llint;
typedef long double lldo;
#define mp make_pair
#define mt make_tuple
#define pub push_back
#define puf push_front
#define pob pop_back
#define pof pop_front
#define fir first
#define sec second
#define res resize
#define ins insert
#define era erase
#define RE return 0
//ios::sync_with_stdio(false);
//std::cin.tie(0);
//<< setprecision(20)
const int mod=(int)1e9+7;
const llint big=(llint)(2.19e15+1);
const long double pai=3.141592653589793238462643383279502884197;
const long double ena=2.71828182845904523536;
const long double eps=1e-7;
template <class T,class U>bool mineq(T& a,U b){if(a>b){a=b;return true;}return false;}
template <class T,class U>bool maxeq(T& a,U b){if(a<b){a=b;return true;}return false;}
template <class T> void soun(T& ar)
{sort(ar.begin(),ar.end());ar.erase(unique(ar.begin(),ar.end()),ar.end());}
llint gcd(llint a,llint b){if(a%b==0){return b;}else{return gcd(b,a%b);}}
llint lcm(llint a,llint b){return a/gcd(a,b) *b;}
template<class T,class U> auto LB(T& ve,U in){return lower_bound(ve.begin(),ve.end(),in);}
template<class T,class U> auto UB(T& ve,U in){return upper_bound(ve.begin(),ve.end(),in);}
template<class T,class U> auto LBI(T& ve,U in){return LB(ve,in)-ve.begin();}
template<class T,class U> auto UBI(T& ve,U in){return UB(ve,in)-ve.begin();}
template<class T> void SO(T& ve){sort(ve.begin(),ve.end());}
template<class T> void REV(T& ve){reverse(ve.begin(),ve.end());}
vector<vector<int>>go;
llint ans=0;
int solve(int ter,int oya){
	int sa=1;
	for(auto it:go[ter]){
		if(it==oya){continue;}
		sa-=solve(it,ter);
	}
	ans+=abs(sa);
	return sa;
}
int main(void){
	int n,m;cin>>n>>m;
	if(m==n){return 0;}
	if(n%2==1){cout<<-1<<endl;return 0;}
	if(n==2){cout<<1<<endl;return 0;}
	//(各辺について、abs(子の葉の偶奇の差))+(葉の数)-n+1
	go.res(n);
	for(int i=0;i<m;i++){
		int a,b;cin>>a>>b;a--;b--;
		go[a].pub(b);go[b].pub(a);
	}
	int sta=0;
	if(go[sta].size()==1){sta=go[sta][0];}
	if(solve(sta,-1)!=0){cout<<-1<<endl;return 0;}
	cout<<ans<<endl;
	RE;
}