#region using
using System;
using System.Collections.Generic;
using System.Linq;
using IEnumerable = System.Collections.IEnumerable;
using IEnumerator = System.Collections.IEnumerator;
using BitArray = System.Collections.BitArray;
using BigInteger = System.Numerics.BigInteger;
using TextReader = System.IO.TextReader;
using System.Text;
#endregion

namespace AtCoderProject
{
    public class Program
    {
        public object Calc()
        {
            var N = consoleReader.Int;
            var M = consoleReader.Int;
            {
                var gb = new GraphBuilder(N);
                foreach (var cr in consoleReader.Repeat(M))
                    gb.Add(cr.Int - 1, cr.Int - 1, cr.Int);
                graph = gb.ToArray();
                var fromStart = CanStart(0);
                gb = new GraphBuilder(N);
                for (int i = 0; i < N; i++)
                    if (fromStart.Contains(i))
                        foreach (var c in graph[i].children)
                            if (fromStart.Contains(c.to))
                                gb.Add(i, c.to, c.length);
                graph = gb.ToArray();
                var canGoal = CanGo(N - 1);
                gb = new GraphBuilder(N);
                for (int i = 0; i < N; i++)
                    if (canGoal.Contains(i))
                        foreach (var c in graph[i].children)
                            if (canGoal.Contains(c.to))
                                gb.Add(i, c.to, c.length);
                graph = gb.ToArray();
            }
            scores = Enumerable.Repeat((long)-1e13, N).ToArray();
            scores[0] = 0;
            sumi = new HashSet<int>();
            loopStatus = new bool[graph.Length];
            try
            {
                CalcScore(0);
                return scores[N - 1];
            }
            catch
            {
                return "inf";
            }
        }

        long[] scores;
        HashSet<int> sumi;
        void CalcScore(int v)
        {
            if (!sumi.Add(v)) return;
            loopStatus[v] = true;
            foreach (var c in graph[v].children)
            {
                long nextScore = scores[v] + c.length;
                if (scores[c.to] < nextScore)
                    if (loopStatus[c.to])
                        throw new Exception();
                    else
                        scores[c.to] = nextScore;
            }
            foreach (var c in graph[v].children)
            {
                CalcScore(c.to);
            }
            loopStatus[v] = false;
        }

        Node[] graph;

        bool[] loopStatus;
        HashSet<int> CanGo(int to) => CanGo(to, new HashSet<int>());
        HashSet<int> CanGo(int to, HashSet<int> result)
        {
            if (result.Add(to))
                foreach (var c in graph[to].roots)
                    CanGo(c.to, result);
            return result;
        }
        HashSet<int> CanStart(int from) => CanStart(from, new HashSet<int>());
        HashSet<int> CanStart(int from, HashSet<int> result)
        {
            if (result.Add(from))
                foreach (var c in graph[from].children)
                    CanStart(c.to, result);
            return result;
        }

        class GraphBuilder
        {
            private List<Next>[] roots;
            private List<Next>[] children;
            public GraphBuilder(int count)
            {
                this.roots = new List<Next>[count];
                this.children = new List<Next>[count];
                for (int i = 0; i < count; i++)
                {
                    this.roots[i] = new List<Next>();
                    this.children[i] = new List<Next>();
                }
            }
            public GraphBuilder(int count, IEnumerable<int[]> arrays) : this(count)
            {
                foreach (var item in arrays)
                    this.Add(item[0], item[1], item[2]);
            }
            public void Add(int from, int to, int length)
            {
                children[from].Add(new Next { to = to, length = length });
                roots[to].Add(new Next { to = from, length = length });
            }
            public Node[] ToArray() =>
                Enumerable
                .Zip(roots, children, (r, c) => Tuple.Create(r, c))
                .Select((t, i) => new Node(i, t.Item1.ToArray(), t.Item2.ToArray()))
                .ToArray();
        }
        public struct Next
        {
            public int to;
            public int length;
        }
        public class Node : IEquatable<Node>
        {
            public Node(int i, Next[] roots, Next[] children)
            {
                this.index = i;
                this.roots = roots;
                this.children = children;
            }
            public int index;
            public Next[] roots;
            public Next[] children;

            public override bool Equals(object obj)
            {
                if (obj is Node)
                    return this.Equals((Node)obj);
                else
                    return false;
            }
            public bool Equals(Node other) => this.index == other.index;
            public override int GetHashCode() => this.index;
        }

        #region いつもの
#pragma warning disable
        private ConsoleReader consoleReader;
        public Program(ConsoleReader consoleReader) { this.consoleReader = consoleReader; }
        static void Main() => Console.WriteLine(new Program(new ConsoleReader(Console.In)).Calc()); static string AllLines<T>(IEnumerable<T> source) => string.Join("\n", source);
    }
    static class Ext
    {
        public static Dictionary<TKey, int> GroupCount<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector) => source.GroupBy(keySelector).ToDictionary(g => g.Key, g => g.Count());
        public static Dictionary<TKey, int> GroupCount<TKey>(this IEnumerable<TKey> source) => source.GroupCount(i => i);
    }
    public class ConsoleReader { private string[] ReadLineSplit() => textReader.ReadLine().Split(Array.Empty<char>(), StringSplitOptions.RemoveEmptyEntries); private string[] line = Array.Empty<string>(); private int linePosition; private TextReader textReader; public ConsoleReader(TextReader tr) { textReader = tr; } public int Int => int.Parse(String); public long Long => long.Parse(String); public double Double => double.Parse(String); public string String { get { if (linePosition >= line.Length) { linePosition = 0; line = ReadLineSplit(); } return line[linePosition++]; } } public class SplitLine { private string[] splited; public SplitLine(ConsoleReader cr) { splited = cr.ReadLineSplit(); cr.line = Array.Empty<string>(); } public int[] Int => String.Select(x => int.Parse(x)).ToArray(); public int[] Int0 => String.Select(x => int.Parse(x) - 1).ToArray(); public long[] Long => String.Select(x => long.Parse(x)).ToArray(); public double[] Double => String.Select(x => double.Parse(x)).ToArray(); public string[] String => splited; } public SplitLine Split => new SplitLine(this); public class RepeatReader : IEnumerable<ConsoleReader> { ConsoleReader cr; int count; public RepeatReader(ConsoleReader cr, int count) { this.cr = cr; this.count = count; } public IEnumerator<ConsoleReader> GetEnumerator() => Enumerable.Repeat(cr, count).GetEnumerator(); System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() => GetEnumerator(); public IEnumerable<string> String => this.Select(cr => cr.String); public IEnumerable<int> Int => this.Select(cr => cr.Int); public IEnumerable<int> Int0 => this.Select(cr => cr.Int - 1); public IEnumerable<long> Long => this.Select(cr => cr.Long); public IEnumerable<double> Double => this.Select(cr => cr.Double); } public RepeatReader Repeat(int count) => new RepeatReader(this, count); }
    #endregion
}


Measured memory_bytes: 13804