#include <vector>
#include <iostream>
#include <cmath>
#include <map>
#include <unordered_map>
#include <algorithm>
#include <fstream>
#include <unistd.h>
#include <string>
#include <numeric>
#include <queue>
#include <deque>
#include <sstream>
#include <iomanip>
#include <set>
#include <stack>
#include <cassert>
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<vvl> vvvl;
typedef vector<vi> vvi;
typedef vector<vvi> vvvi;
typedef vector<bool> vb;
typedef vector<vector<bool>> vvb;
typedef vector<vvb> vvvb;
typedef vector<vvvb> vvvvb;
typedef vector<string> vs;
typedef vector<vs> vvs;
typedef vector<vvs> vvvs;
typedef vector<char> vc;
typedef vector<vector<char>> vvc;
typedef vector<double> vd;
typedef vector<vd> vvd;
typedef vector<vvd> vvvd;
typedef pair<ll, ll> PL;
typedef vector<PL> vpl;
typedef vector<vector<PL>> vvpl;
const int INF = 1001001001;
const ll LINF = 1e17;
const double pi = 3.1415926535897932;
const string endstr = "\n";
#define FOR(i, a, b) for(ll i = (a); i < b; i++)
#define RFOR(i, a, b) for(ll i = (a); i > b; i--)
#define rep(i, n) for(ll i = 0; i < n; i++)
#define rrep(i, n) for(ll i = n-1; i > -1; i--)
#define FORMAP(it, m) for(auto it = m.begin(); it != m.end(); it++)
#define ff first
#define ss second
#define pb push_back
#define epb emplace_back

template <typename T>
T gcd(T a, T b) {
    return (a == 0) ? b : gcd(b%a, a);
}
template <typename T>
T lcm(T a, T b) {
    return a / gcd(a, b) * b;
}

bool p_comp_fs(const PL p1, const PL p2){ return p1.first < p2.first;};
bool p_comp_fg(const PL p1, const PL p2){ return p1.first > p2.first;};
bool p_comp_ss(const PL p1, const PL p2){ return p1.second < p2.second;};
bool p_comp_sg(const PL p1, const PL p2){ return p1.second > p2.second;};
template <typename T>
vector<T> uniquen(vector<T> vec){
    vec.erase(unique(vec.begin(), vec.end()), vec.end());
    return vec;
}

inline ll popcnt(ll x){return __builtin_popcount((unsigned int)x);};
template<class T> bool chmax(T &a, T b) { if (a < b) { a = b; return true; } return false; }
template<class T> bool chmin(T &a, T b) { if (a > b) { a = b; return true; } return false; }

struct edge{ll to, sum;};

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    ll N, M; cin >> N >> M;
    vector<edge> G[N];
    rep(i, M){
        ll u, v, s; cin >> u >> v >> s; u--; v--;
        G[u].pb({v, s});
        G[v].pb({u, s});
    }
    
    queue<PL> q;
    vvl dist(N, vl(2, -LINF)); dist[0][1] = 1;
    q.push({0,1});
    while(!q.empty()){
        ll now = q.front().ff, pm = q.front().ss; q.pop();
        for(auto e : G[now]){
            if(dist[e.to][1-pm] != -LINF){
                if(dist[e.to][1-pm] != e.sum - dist[now][pm]){
                    cout << 0 << endstr;
                    return 0;
                }
            }
            else{
                dist[e.to][1-pm] = e.sum - dist[now][pm];
                q.push({e.to, 1-pm});
            }
        }
    }
    
    ll diff = -LINF;
    rep(i, N){
        if(dist[i][1] == -LINF || dist[i][0] == -LINF) continue;
        if(diff == -LINF){
            diff = dist[i][1] - dist[i][0];
        }
        else{
            if(diff != dist[i][1] - dist[i][0]){
                cout << 0 << endstr; return 0;
            }
        }
    }
    if(diff != -LINF){
        if(diff%2 == 0){
            bool ok = true;
            rep(i, N){
                if(dist[i][1] == -LINF || dist[i][0] == -LINF) continue;
                if((dist[i][1]+dist[i][0])/2 <= 0){
                    ok = false; break;
                }
            }
            cout << (ok ? 1 : 0) << endstr; return 0;
        }
        else{
            cout << 0 << endstr; return 0;
        }
    }
    
    ll mnp = LINF,mnm = LINF;
    rep(i, N){
        if(dist[i][1] != -LINF){
            chmin(mnp, dist[i][1]);
        }
        if(dist[i][0] != -LINF){
            chmin(mnm, dist[i][0]);
        }
    }
    
    if(mnp * mnm < 0){
        ll mn = min(mnp, mnm), mx = max(mnp, mnm);
        if(abs(mn) >= abs(mx)) cout << 0 << endstr;
        else{
            cout << abs(abs(mn)-abs(mx))-1 << endstr;
        }
    }
    else if(mnp == 0 && mnm > 0){
        cout << mnm-1 << endstr;
    }
    else if(mnp > 0 && mnm == 0){
        cout << mnp-1 << endstr;
    }
    else if(mnp > 0 && mnm > 0){
        cout << mnm + mnp - 1 << endstr;
    }
    else{
        cout << 0 << endstr;
    }
    cerr << "test" << endstr;
    return 0;
}


Measured memory_bytes: 14448