#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef unsigned int uint;
typedef unsigned char uchar;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;

#define REP(i,x) for(int i=0;i<(int)(x);i++)
#define REPS(i,x) for(int i=1;i<=(int)(x);i++)
#define RREP(i,x) for(int i=((int)(x)-1);i>=0;i--)
#define RREPS(i,x) for(int i=((int)(x));i>0;i--)
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();i++)
#define RFOR(i,c) for(__typeof((c).rbegin())i=(c).rbegin();i!=(c).rend();i++)
#define ALL(container) (container).begin(), (container).end()
#define RALL(container) (container).rbegin(), (container).rend()
#define SZ(container) ((int)container.size())
#define mp(a,b) make_pair(a, b)
#define pb push_back
#define eb emplace_back
#define UNIQUE(v) v.erase( unique(v.begin(), v.end()), v.end() );
#define __builtin_popcount __builtin_popcountll

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 (a>b) { a=b; return 1; } return 0; }
template<class T> ostream& operator<<(ostream &os, const vector<T> &t) {
    os<<"["; FOR(it,t) {if(it!=t.begin()) os<<","; os<<*it;} os<<"]"; return os;
}
template<class T> ostream& operator<<(ostream &os, const set<T> &t) {
    os<<"{"; FOR(it,t) {if(it!=t.begin()) os<<","; os<<*it;} os<<"}"; return os;
}
template<class S, class T> ostream& operator<<(ostream &os, const pair<S,T> &t) { return os<<"("<<t.first<<","<<t.second<<")";}
template<class S, class T> pair<S,T> operator+(const pair<S,T> &s, const pair<S,T> &t){ return pair<S,T>(s.first+t.first, s.second+t.second);}
template<class S, class T> pair<S,T> operator-(const pair<S,T> &s, const pair<S,T> &t){ return pair<S,T>(s.first-t.first, s.second-t.second);}

const int INF = 1<<28;
const double EPS = 1e-8;
const int MOD = 1000000007;


int T, n, m;
vector<vector<pii>> g;
vector<ll> level;
vector<ll> w;
ll rootValue = 0;
int hasOdd = 0;
int dfs(int u, int p) {
    level[u] = p == -1 ? 1 : level[p] + 1;
    for(auto e : g[u]) {
        int v, s; tie(v, s) = e;
        if (v == p) continue;
        if (!level[v]) { // not visited
            w[v] = s - w[u];
            dfs(v, u);
        } else if(level[v] % 2 != level[u] % 2) { // even cycle
            if (w[u] + w[v] != s) {
                cout << 0 << endl;
                exit(0);
            }
        } else { // odd cycle
            hasOdd = 1;
            if (w[u] + w[v] != s) {
                if (w[0] != 0 || (w[u] + w[v] - s) % 2 != 0) {
                    cout << 0 << endl;
                    exit(0);
                }
                rootValue = abs((w[u] + w[v] - s) / 2);
            }
        }
    }
}

int main(int argc, char *argv[]){
    ios::sync_with_stdio(false);
    cin >> n >> m;
    g.resize(n);
    level.resize(n);
    w.resize(n);
    REP(i, m) {
        int u, v, a;
        cin >> u >> v >> a; u--; v--;
        g[u].emplace_back(v, a);
        g[v].emplace_back(u, a);
    }
    dfs(0, -1);
    level = vector<ll>(n);
    w = vector<ll>(n);
    w[0] = rootValue;
    dfs(0, -1);
    vector<ll> mins(2, 1ll << 60);
    REP(i, n) {
        chmin(mins[level[i] % 2], w[i]);
    }
    ll ans = max(0ll, mins[1] + mins[0] - 1);
    if (hasOdd) ans = mins[0] > 0 && mins[1] > 0;
    cout << ans << endl;
    return 0;
}


Measured memory_bytes: 12032