#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;

struct d {
    int c = -10001;
};

vector<int> color, prev1;
vector<unordered_set<int>> g;
unordered_map<int, unordered_map<int, d>> cost;
int cycle_start, cycle_end;

int ans = -INT_MAX, cnt = 0;
vector<bool> vis;

bool dfs1(int u, int n) {
    vis[u] = true;
    if (u == n) {
        return true;
    }
    for (auto v : g[u]) {
        if (!vis[v]) {
            cnt += cost[u][v].c;
            ans = max(ans, cnt);
            return dfs1(v, n);
        }
    }
    return false;
}

bool dfs2 (int u) {
    color[u] = 1;
    for (auto v : g[u]) {
        if (color[v] == 0) {
            prev1[v] = u;
            if (dfs2(v)) {
                return true;
            }
        }
        else if (color[v] == 1) {
            cycle_end = u;
            cycle_start = v;
            return true;
        }
    }
    color[u] = 2;
    return false;
}

void solve() {
    ios::sync_with_stdio(false);
    cin.tie(NULL);

    int n, m;
    cin >> n >> m;
    g.resize(n);
    color.resize(n);
    vis.resize(n);
    prev1.resize(n);

    bool lotknow = false;
    for (int i = 0; i < m; i++) {
        int a, b, c;
        cin >> a >> b >> c;
        --a, --b;
        g[a].insert(b);
        cost[a][b].c = max(cost[a][b].c, c);
        if (a == b && cost[a][b].c > 0) {
            lotknow = true;
        }
    }
    cycle_start = -1;
    if (!dfs1(0, n - 1)) {
        cout << ":(";
    }
    else {
        if (lotknow) {
            cout << ":)";
            return;
        }
        for (int i = 0; i < n - 1; i++) {
            color.assign(n - 1, 0);
            if (dfs2(i)) {
                vector<int> cycle_path;
                cycle_path.push_back(cycle_start);

                for (int v = cycle_end; v != cycle_start; v = prev1[v]) {
                    cycle_path.push_back(v);
                }

                int sum = 0;

                for (int i1 : cycle_path) {
                    sum += i1;
                }
                if (sum <= 0) {
                    cout << ans;
                    return;
                }
            }
        }
        if (cycle_start != -1) {
            cout << ":)";
            return;
        }
        else {
            cout << ans;
        }
    }
}

int main() {
    solve();
    return 0;
}