//header
#ifdef LOCAL
    #include "cxx-prettyprint-master/prettyprint.hpp"
    #define print(x) cout << x << endl
#else
    #define print(...) 42
#endif
    #pragma GCC optimize("Ofast")
    #include <bits/stdc++.h>
    //types
    using namespace std;
    using ll = long long;
    typedef pair < ll , ll >P;
    typedef vector<ll> vl;
    template< typename T >
    using mat = vector< vector< T > >;
    template <std::uint_fast64_t Modulus> class modint {
        using u64 = std::uint_fast64_t;

        public:
        u64 a;

        constexpr modint(const u64 x = 0) noexcept : a(x % Modulus) {}
        constexpr u64 &value() noexcept { return a; }
        constexpr const u64 &value() const noexcept { return a; }
        constexpr modint operator+(const modint rhs) const noexcept {
            return modint(*this) += rhs;
        }
        constexpr modint operator-(const modint rhs) const noexcept {
            return modint(*this) -= rhs;
        }
        constexpr modint operator*(const modint rhs) const noexcept {
            return modint(*this) *= rhs;
        }
        constexpr modint operator/(const modint rhs) const noexcept {
            return modint(*this) /= rhs;
        }
        constexpr modint &operator+=(const modint rhs) noexcept {
            a += rhs.a;
            if (a >= Modulus) {
            a -= Modulus;
            }
            return *this;
        }
        constexpr modint &operator-=(const modint rhs) noexcept {
            if (a < rhs.a) {
            a += Modulus;
            }
            a -= rhs.a;
            return *this;
        }
        constexpr modint &operator*=(const modint rhs) noexcept {
            a = a * rhs.a % Modulus;
            return *this;
        }
        constexpr modint &operator/=(modint rhs) noexcept {
            u64 exp = Modulus - 2;
            while (exp) {
            if (exp % 2) {
                *this *= rhs;
            }
            rhs *= rhs;
            exp /= 2;
            }
            return *this;
        }
        };
    //abbreviations
    #define all(x) (x).begin(), (x).end()
    #define reverse(x) (x).rbegin(), (x).rend()
    #define rep2(i,a,b) for(ll i=(a);i<(b);++i)
    #define rep(i,n) for(ll i=0;i<(n);++i)
    #define SZ(x) ((ll)(x).size())
    #define pb(x) push_back(x)
    #define ff first
    #define ss second
    #define mp make_pair
    //functions
    ll gcd(ll a, ll b) { return b ? gcd(b, a%b) : a; }
    template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
    template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
    template< typename T >
    T mypow(T x, ll n) {
        T ret = 1;
        while(n > 0) {
            if(n & 1) (ret *= x);
            (x *= x);
            n >>= 1;
        }
        return ret;
    }
    uint64_t my_rand(void) {
        static uint64_t x = 88172645463325252ULL;
        x = x ^ (x << 13); x = x ^ (x >> 7);
        return x = x ^ (x << 17);
    }
    //graph template
    template< typename T >
    struct edge {
        int src, to;
        T cost;

        edge(int to, T cost) : src(-1), to(to), cost(cost) {}

        edge(int src, int to, T cost) : src(src), to(to), cost(cost) {}

        edge &operator=(const int &x) {
        to = x;
        return *this;
    }

    operator int() const { return to; }
    };

    template< typename T >
    using Edges = vector< edge< T > >;
    template< typename T >
    using WeightedGraph = vector< Edges< T > >;
    using UnWeightedGraph = vector< vector< int > >;

//constant
#define INF 1'010'000'000'000'000'017LL
#define mod 1000003LL
typedef modint<mod> mint;
#define eps 0.000001
//library

//main
int main(){
    int n, m;
    cin>>n>>m;
    WeightedGraph<ll> G(n);
    rep(i, m){
        ll u, v, s;
        cin>>u>>v>>s;
        G[u-1].pb(edge<ll>(v-1, s));
        G[v-1].pb(edge<ll>(u-1, s));
    }
    vl color(n, -1), value(n, -1);
    color[0] = 0;
    value[0] = 0;
    deque<ll> que; que.pb(0);
    ll diff = 0;
    bool flag = true;
    while(SZ(que)){
        ll v = que.front();
        que.pop_front();
        ll c = color[v];
        ll val = value[v];
        for(auto e:G[v]){
            if(color[e.to] == c){
                diff = value[e.to]-(e.cost-val);
                flag = false;
                break;
            }
            if(color[e.to] == -1){
                value[e.to] = e.cost-val;
                color[e.to] = 1-c;
                que.pb(e.to);
            }
        }
    } 
    rep(i, n){
        for(auto e:G[i]){
            if(color[i] == color[e.to])flag = false;
            if(color[i]!=0&&color[i]!=1) flag = false;
        }
    }
    if(not flag){
        diff = abs(diff);
        if(diff%2 != 0 || diff == 0){
            cout << 0 << endl;
            return 0;
        }
        rep(i, n)value[i] = -1;
        value[0] = abs(diff)/2;
        deque<ll> que; que.pb(0);
        while(SZ(que)){
            ll v = que.front();
            que.pop_front();
            ll val = value[v];
            for(auto e:G[v]){
                if(value[e.to] != -1){
                    if(value[e.to]+val == e.cost)continue;
                    cout << 0 <<endl;
                    return 0;
                }
                value[e.to] = e.cost-val;
                que.pb(e.to);
                if(value[e.to]<=0){
                    cout << 0 << endl;
                    return 0;
                }
            }
        } 
        flag = true;
        rep(i, n){
            if(value[i]<=0)flag = false;
            for(auto e:G[i]){
                if(value[i]+value[e.to]!=e.cost) flag = false;
            }
        }
        if(flag) cout << 1 << endl;
        else cout << 0 << endl;
        return 0;
    }
    if(diff>0)throw "anb";
    ll a = INF, b = INF;
    rep(i, n){
        int c = color[i];
        if(c == 0)chmin(a, value[i]);
        else chmin(b, value[i]);
    }
    rep(i, n)value[i] = -1;
    value[0] = abs(a)+1;
    que.pb(0);
    if(a<=0){
    while(SZ(que)){
        ll v = que.front();
        que.pop_front();
        ll val = value[v];
        for(auto e:G[v]){
            if(value[e.to] != -1){
                if(value[e.to]+val == e.cost)continue;
                cout << 0 <<endl;
                return 0;
            }
            value[e.to] = e.cost-val;
            que.pb(e.to);
            if(value[e.to]<=0){
                cout << 0 << endl;
                return 0;
            }
        }
    }
    }
    cout << max(0, int(a+b-1))<< endl;
    return 0;
}


Measured memory_bytes: 9728