#include<bits/stdc++.h>
#define rep(i,a,...) for(int i = (a)*(strlen(#__VA_ARGS__)!=0);i<(int)(strlen(#__VA_ARGS__)?__VA_ARGS__:(a));++i)
#define per(i,a,...) for(int i = (strlen(#__VA_ARGS__)?__VA_ARGS__:(a))-1;i>=(int)(strlen(#__VA_ARGS__)?(a):0);--i)
#define foreach(i, n) for(auto &i:(n))
#define all(x) (x).begin(), (x).end()
#define bit(x) (1ll << (x))
#define lambda(RES_TYPE, ...) (function<RES_TYPE(__VA_ARGS__)>)[&](__VA_ARGS__) -> RES_TYPE
#define method(FUNC_NAME, RES_TYPE, ...) function<RES_TYPE(__VA_ARGS__)> FUNC_NAME = lambda(RES_TYPE, __VA_ARGS__)
using namespace std;
using ll = long long;
using pii = pair<int,int>;
using pll = pair<ll,ll>;
//const ll MOD = (ll)1e9+7;
const ll MOD = 998244353;
const int INF = (ll)1e9+7;
const ll INFLL = (ll)1e18;
template<class t>
using vvector = vector<vector<t>>;
template<class t>
using vvvector = vector<vector<vector<t>>>;
template<class t>
using priority_queuer = priority_queue<t, vector<t>, greater<t>>;
template<class t, class u> bool chmax(t &a, u b){if(a<b){a=b;return true;}return false;}
template<class t, class u> bool chmin(t &a, u b){if(a>b){a=b;return true;}return false;}
#ifdef DEBUG
#define debug(x) cout<<"LINE "<<__LINE__<<": "<<#x<<" = "<<x<<endl;
#else
#define debug(x) (void)0
#endif

namespace templates{
  ll modpow(ll x, ll b){
    ll res = 1;
    while(b){
      if(b&1)res = res * x % MOD;
      x = x * x % MOD;
      b>>=1;
    }
    return res;
  }

  ll modinv(ll x){
    return modpow(x, MOD-2);
  }

  bool was_output = false;
  template<class t>
  void output(t a){
    if(was_output)cout << " ";
    cout << a;
    was_output = true;
  }
  void outendl(){
    was_output = false;
    cout << endl;
  }
  ll in(){
    ll res;
    scanf("%lld", &res);
    return res;
  }

  template<class t>
  istream& operator>>(istream&is, vector<t>&x){
    for(auto &i:x)is >> i;
    return is;
  }

  template<class t, class u>
  istream& operator>>(istream&is, pair<t, u>&x){
    is >> x.first >> x.second;
    return is;
  }

  template<class t>
  void in(t&x){
    cin >> x;
  }

  template<class t>
  t in(){
    t res; cin >> res; return res;
  }

  template<class t>
  void out(t x){
    cout << x;
  }

  template<class t>
  vector<t> sorted(vector<t> line,function<bool(t,t)> comp=[](t a,t b){return a<b;}){
    sort(line.begin(),line.end(),comp);
    return line;
  }

  template<class t>
  vector<t> reversed(vector<t> line){
    reverse(line.begin(),line.end());
    return line;
  }
}

using namespace templates;

ll func(){
    int n = in();
    int m = in();
    vvector<pll> edges(n);
    rep(i,m){
        int a = in()-1;
        int b = in()-1;
        int c = in();
        edges[a].emplace_back(b,c);
        edges[b].emplace_back(a,c);
    }

    vector<ll> t_plus(n,INFLL);
    vector<ll> t_minus(n,INFLL);

    method(func,void,int place,ll sum,bool is_plus){
        vector<ll> &current = (is_plus?t_plus:t_minus);
        if(current[place]!=INFLL){
            if(current[place]==sum)return;
            t_minus[place] = -INFLL;
            return;
        }
        current[place] = sum;
        foreach(i,edges[place]){
            func(i.first,i.second-sum,!is_plus);
        }
    };
    func(edges[0][0].first,edges[0][0].second,false);
    ll lower = -INFLL;
    ll upper = INFLL;
    rep(i,n){
        if(t_plus[i]==INFLL and t_minus[i]==INFLL)continue;
        chmax(lower,-t_plus[i]+1);
        chmin(upper,t_minus[i]-1);
        if(t_plus[i]!=INFLL and t_minus[i]!=INFLL){
            ll dis = t_minus[i] - t_plus[i];
            if(dis%2==1){
                return 0;
            }
            ll mid = (t_minus[i] - t_plus[i]) / 2;
            chmax(lower,mid);
            chmin(upper,mid);
        }
    }
    return max(0LL,upper-lower+1);
}

int main(){
    cout << func() << endl;
    return 0;
}


Measured memory_bytes: 26596