#include<bits/stdc++.h>
using namespace std;

const int N = 200009;
typedef long long LL;

inline int read() {
    int x = 0; char fs = 0, c = getchar();
    while(! isdigit(c)) fs |= (c == '-'), c = getchar();
    while(isdigit(c)) x = (x << 1) + (x << 3) + (c ^ 48), c = getchar();
    return fs ? -x : x;
}

int n, m;
int h[N], ne[N << 1], to[N << 1], w[N << 1], tot;
int siz[N], a[N];
int sum, flag;

inline void add(int x, int y, int v) {
    ne[++ tot] = h[x], h[x] = tot, to[tot] = y, w[tot] = v;
}

void F(int p, int x) {
    sum += a[x];
    siz[x] = 1;
    for(int i = h[x]; i; i = ne[i]) {
        int y = to[i], v = w[i] >> p & 1;
        if(siz[y]) {
            if(a[y] ^ a[x] ^ v) flag = 1;
            continue;
        }
        a[y] = a[x] ^ v;
        F(p, y);
        siz[x] += siz[y];
    }
}


int main() {
    n = read(), m = read();
    for(int i = 1; i <= m; i ++) {
        int x = read(), y = read(), v = read();
        add(x, y, v), add(y, x, v);
    }
    LL ans = 0;
    for(int p = 0; p <= 29; p ++) {
        memset(siz, 0, sizeof siz);
        for(int i = 1; i <= n; i ++) if(! siz[i]) {
            sum = 0;
            F(p, i);
            ans += (1ll << p) * min(siz[i] - sum, sum);
        }
    }
    if(flag) ans = -1;
    printf("%lld\n", ans);
    return 0;
}