#include <bits/stdc++.h>
#define Ciallo main
using namespace std;
const int N = 4e6;

inline int read(){
    int _x = 0, _w = 1;
    char ch = 0;
    while(ch < '0' || ch > '9') {
        if(ch == '-') _w = -1;
#ifdef __linux__
        ch = (char)getchar_unlocked();
#else
        ch = (char) _getchar_nolock();
#endif
    }
    while(ch >= '0' && ch <= '9') {
        _x = (_x << 3) + (_x << 1) + (ch - '0');
#ifdef __linux__
        ch = (char)getchar_unlocked();
#else
        ch = (char) _getchar_nolock();
#endif
    }
    return _x * _w;
}

inline void write(int _x){
    if(_x < 0) {
#ifdef __linux__
        putchar_unlocked('-');
#else
        _putchar_nolock('-');
#endif
        _x = -_x;
    }
    static int _sta[130];
    int _top = 0;
    do {
        _sta[_top++] = _x % 10, _x /= 10;
    } while(_x);
    while(_top)
#ifdef __linux__
        putchar_unlocked(_sta[--_top] + 48);
    putchar_unlocked('\n');
#else
        _putchar_nolock(_sta[--_top] + 48);
    _putchar_nolock('\n');
#endif
}

int n, m, sum, x, y, z;
int e[N], h[N], ne[N], idx, p[N];
int w[N], cnt;
int q[N], d[N], hh, tt;

inline void add(int _a, int _b, int _c){
    e[idx] = _b, p[idx] = _c, ne[idx] = h[_a], h[_a] = idx++;
}

void topoSort(){
    for(int i = 1; i <= n + cnt; i++)
        if(!d[i]) {
            q[tt++] = i;
            w[i] = 1;
        }

    while(hh < tt) {
        int t = q[hh++];
        for(int i = h[t]; i != -1; i = ne[i]) {
            int j = e[i];
            w[j] = max(w[j], w[t] + w[p[i]]);
            d[j]--;
            if(!d[j])
                q[tt++] = j;
        }
    }
}

signed Ciallo(){
    memset(h, -1, sizeof h);
    n = read(), m = read();
    while(m--) {
        x = read(), y = read(), z = read();
        if(x == y || x == z){
            puts("-1");
            return 0;
        }
        add(y, x, z), add(z, x, y);
        d[x] += 2;
    }

    topoSort();
    for(int i = 1; i <= n; i++)
//        write(w[i]);
        sum += w[i];
    write(sum);

    return 0;
}