#include <bits/stdc++.h>
#define LLI long long int
#define FOR(v, a, b) for(LLI v = (a); v < (b); ++v)
#define FORE(v, a, b) for(LLI v = (a); v <= (b); ++v)
#define REP(v, n) FOR(v, 0, n)
#define REPE(v, n) FORE(v, 0, n)
#define REV(v, a, b) for(LLI v = (a); v >= (b); --v)
#define ALL(x) (x).begin(), (x).end()
#define RALL(x) (x).rbegin(), (x).rend()
#define ITR(it, c) for(auto it = (c).begin(); it != (c).end(); ++it)
#define RITR(it, c) for(auto it = (c).rbegin(); it != (c).rend(); ++it)
#define EXIST(c,x) ((c).find(x) != (c).end())
#define fst first
#define snd second
#define popcount __builtin_popcount
#define UNIQ(v) (v).erase(unique(ALL(v)), (v).end())
#define bit(i) (1LL<<(i))

#ifdef DEBUG
#include <misc/C++/Debug.cpp>
#else
#define dump(...) ((void)0)
#endif

#define gcd __gcd

using namespace std;
template <class T> constexpr T lcm(T m, T n){return m/gcd(m,n)*n;}

template <typename I> void join(ostream &ost, I s, I t, string d=" "){for(auto i=s; i!=t; ++i){if(i!=s)ost<<d; ost<<*i;}ost<<endl;}
template <typename T> istream& operator>>(istream &is, vector<T> &v){for(auto &a : v) is >> a; return is;}

template <typename T, typename U> bool chmin(T &a, const U &b){return (a>b ? a=b, true : false);}
template <typename T, typename U> bool chmax(T &a, const U &b){return (a<b ? a=b, true : false);}
template <typename T, size_t N, typename U> void fill_array(T (&a)[N], const U &v){fill((U*)a, (U*)(a+N), v);}

template <typename Cost = int> class Edge{
public:
  int from,to;
  Cost cost;
  Edge() {}
  Edge(int to, Cost cost): to(to), cost(cost){}
  Edge(int from, int to, Cost cost): from(from), to(to), cost(cost){}

  Edge rev() const {return Edge(to,from,cost);}
  
  friend ostream& operator<<(ostream &os, const Edge &e){
    os << "(FROM: " << e.from << "," << "TO: " << e.to << "," << "COST: " << e.cost << ")";
    return os;
  }
};

template <typename T> using Graph = vector<vector<Edge<T>>>;
template <typename T> using Tree = vector<vector<Edge<T>>>;

template <typename C, typename T> void add_edge(C &g, int from, int to, T w){
  g[from].push_back(Edge<T>(from, to, w));  
}

template <typename C, typename T> void add_undirected(C &g, int a, int b, T w){
  g[a].push_back(Edge<T>(a, b, w));
  g[b].push_back(Edge<T>(b, a, w));
}

Graph<int> g;

int parity[100100];
bool visited[100100];
LLI memo[100100];


bool dfs(int cur){
  visited[cur] = true;

  for(auto &e : g[cur]){
    if(visited[e.to]){
      if(parity[cur] == parity[e.to]){
        return false;
      }
    }

    parity[e.to] = !parity[cur];

    if(not visited[e.to]){
      if(not dfs(e.to)) return false;
    }
  }
  
  return true;
}

bool dfs2(int cur){
  visited[cur] = true;

  for(auto &e : g[cur]){
    if(visited[e.to]){
      if(e.cost != memo[cur] + memo[e.to]){
        return false;
      }
    }

    memo[e.to] = e.cost - memo[cur];

    if(not visited[e.to]){
      if(not dfs2(e.to)) return false;
    }
  }

  return true;
}

bool visited2[100100][2];
LLI memo2[1001000][2];

void dfs3(int cur, int p){
  visited2[cur][p] = true;

  for(auto &e : g[cur]){
    if(not visited2[e.to][!p]){
      memo2[e.to][!p] = e.cost - memo2[cur][p];
      dfs3(e.to, !p);
    }
  }
}

bool dfs4(int cur){
  if(memo[cur] <= 0) return false;
  visited[cur] = true;

  for(auto &e : g[cur]){
    if(visited[e.to]){
      if(e.cost != memo[cur] + memo[e.to]){
        return false;
      }
    }

    memo[e.to] = e.cost - memo[cur];

    if(not visited[e.to]){
      if(not dfs4(e.to)) return false;
    }
  }

  return true;
}




int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);

  int n,m;
  while(cin >> n >> m){
    g = Graph<int>(n);

    REP(i,m){
      int u,v,s; cin >> u >> v >> s;
      --u, --v;
      add_undirected(g,u,v,s);
    }

    fill_array(parity, -1);
    fill_array(visited, false);
    fill_array(memo, 0);

    parity[0] = 0;

    LLI ans = -1;

    if(dfs(0)){
      fill_array(visited, false);

      if(dfs2(0)){
        LLI lb=0,ub=INT_MAX;
        REP(i,n){
          if(parity[i] == 0){
            chmax(lb, 1-memo[i]);
          }else{
            chmin(ub, memo[i]-1);
          }
        }
        ans = max(0LL, ub-lb+1);
      }else{
        ans = 0;
      }
    }else{
      fill_array(visited2, false);
      fill_array(memo2, 0);
      
      dfs3(0,0);

      LLI t = (memo2[0][0] + memo2[0][1]) / 2;

      fill_array(visited, false);

      memo[0] = t;
      if(dfs4(0)){
        ans = 1;
      }else{
        ans = 0;
      }
    }

    cout << ans << endl;    
  }
  
  return 0;
}


Measured memory_bytes: 29824