#include<bits/stdc++.h>
using namespace std;

#define ALL(a)  (a).begin(),(a).end()
#define ALLR(a)  (a).rbegin(),(a).rend()
#define spa << " " <<
#define lfs <<fixed<<setprecision(10)<<
#define test cout<<"test"<<endl;
#define fi first
#define se second
#define MP make_pair
#define PB push_back
#define EB emplace_back
#define rep(i,n,m) for(ll i = n; i < (ll)(m); i++)
#define rrep(i,n,m) for(ll i = n - 1; i >= (ll)(m); i--)
typedef long long ll;
typedef long double ld;
const ll MOD = 1e9+7;
//const ll MOD = 998244353;
const ll INF = 1e18;
using P = pair<ll, ll>;
template<typename T>
void chmin(T &a,T b){if(a>b)a=b;}
template<typename T>
void chmax(T &a,T b){if(a<b)a=b;}
void pmod(ll &a,ll b){a=(a+b)%MOD;}
void pmod(ll &a,ll b,ll c){a=(b+c)%MOD;}
void qmod(ll &a,ll b){a=(a*b)%MOD;}
void qmod(ll &a,ll b,ll c){a=(b*c)%MOD;}
ll median(ll a,ll b, ll c){return a+b+c-max({a,b,c})-min({a,b,c});}
void ans1(bool x){if(x) cout<<"Yes"<<endl;else cout<<"No"<<endl;}
void ans2(bool x){if(x) cout<<"YES"<<endl;else cout<<"NO"<<endl;}
void ans3(bool x){if(x) cout<<"Yay!"<<endl;else cout<<":("<<endl;}
template<typename T1,typename T2>
void ans(bool x,T1 y,T2 z){if(x)cout<<y<<endl;else cout<<z<<endl;}  
template<typename T>
void debug(vector<vector<T>>v,ll h,ll w){for(ll i=0;i<h;i++)
{cout<<v[i][0];for(ll j=1;j<w;j++)cout spa v[i][j];cout<<endl;}};
void debug(vector<string>v,ll h,ll w){for(ll i=0;i<h;i++)
{for(ll j=0;j<w;j++)cout<<v[i][j];cout<<endl;}};
template<typename T>
void debug(vector<T>v,ll n){cout<<v[0];
for(ll i=1;i<n;i++)cout spa v[i];cout<<endl;};
template<typename T>
vector<vector<T>>vec(ll x, ll y, T w){
  vector<vector<T>>v(x,vector<T>(y,w));return v;}
ll gcd(ll x,ll y){ll r;while(y!=0&&(r=x%y)!=0){x=y;y=r;}return y==0?x:y;}
template<typename T>
void emp(map<T,ll>&m, T x){m.emplace(x,0).first->second++;}

ll MAX_V = 2e5 + 5;
struct edge {
  ll to,cost;
  edge(ll x,ll y):to(x),cost(y){};
};

vector<vector<struct edge>> G(MAX_V);
vector<ll>t(MAX_V,-1);//深さ
vector<ll>s(MAX_V,-1);
ll le=0,ri=INF;
void dfs(ll k,ll d, ll x){
  t[k]=d;
  s[k]=x;
  if(d%2==0){
    if(x<=0)chmax(le,-x+1);
  }
  else{
    chmin(ri,x-1);
  }
  for(ll i=0;i<G[k].size();i++){
    if(t[G[k][i].to]==-1){
      dfs(G[k][i].to,d+1,G[k][i].cost - x); 
    }
  }
}

int main(){
  cin.tie(NULL);
  ios_base::sync_with_stdio(false);
  ll res=0,res1=INF,res2=-INF,buf=0;
  bool judge = true;
  ll n,m;cin>>n>>m;
  vector<ll>u(m),v(m),c(m);
  for(ll i=0;i<m;i++){
    cin>>u[i]>>v[i]>>c[i];
    u[i]--;v[i]--;
    G[u[i]].emplace_back(v[i],c[i]);
    G[v[i]].emplace_back(u[i],c[i]);
  }
  dfs(0,0,1);
  rep(i,0,m){
    if(t[u[i]]%2!=t[v[i]]%2){
      if(s[u[i]]+s[v[i]]!=c[i]){
        ri=-1;
      }
    }
    else{
      if(s[u[i]]+s[v[i]]==c[i]){
        chmin(ri,0LL);
      }
      else{
        ll x=c[i]-(s[u[i]]+s[v[i]]);
        if(t[u[i]]%2==0){
          if(x<0||x%2==1)ri=-1;
          else{
            chmax(le,x/2);
            chmin(ri,x/2);
          }
        }
        else{
          if(x>0||x%2==1)ri=-1;
          else{
            chmax(le,-x/2);
            chmin(ri,-x/2);
          }
        }
      }
    }
  }
  //cout<<le spa ri<<endl;
  //debug(t,3);
  cout<<max(0LL,ri-le+1)<<endl;
  return 0;
}

Measured memory_bytes: 20352