using AtCoderBeginnerContest153.Questions;
using AtCoderBeginnerContest153.Extensions;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;

namespace AtCoderBeginnerContest153.Questions
{
    public class QuestionE : AtCoderQuestionBase
    {
        public override IEnumerable<object> Solve(TextReader inputStream)
        {
            var hn = inputStream.ReadIntArray();
            var h = hn[0];
            var n = hn[1];

            var magics = new Magic[n];
            for (int i = 0; i < magics.Length; i++)
            {
                var ab = inputStream.ReadIntArray();
                magics[i] = new Magic(ab[0], ab[1]);
            }

            var dpMinMP = Enumerable.Repeat(long.MaxValue >> 4, h + magics.Max(m => m.Attack)).ToArray();   // オーバーキルの可能性あり
            dpMinMP[0] = 0; // init

            for (int totalDamage = 1; totalDamage < dpMinMP.Length; totalDamage++)
            {
                foreach (var magic in magics)
                {
                    var previousTotalDamage = totalDamage - magic.Attack;

                    if (previousTotalDamage >= 0)
                    {
                        UpdateWhenSmall(ref dpMinMP[totalDamage], dpMinMP[previousTotalDamage] + magic.MP);
                    }
                }
            }

            var minMP = long.MaxValue;
            for (int i = h; i < dpMinMP.Length; i++)
            {
                if (dpMinMP[i] < minMP)
                {
                    minMP = dpMinMP[i];
                }
            }

            yield return minMP;
        }

        protected void UpdateWhenSmall<T>(ref T value, T other) where T : IComparable<T>
        {
            if (other.CompareTo(value) < 0)
            {
                value = other;
            }
        }

        protected void UpdateWhenLarge<T>(ref T value, T other) where T : IComparable<T>
        {
            if (other.CompareTo(value) > 0)
            {
                value = other;
            }
        }
    }

    public struct Magic
    {
        public int Attack { get; }
        public int MP { get; }

        public Magic(int attack, int mp)
        {
            Attack = attack;
            MP = mp;
        }
    }
}


namespace AtCoderBeginnerContest153
{
    class Program
    {
        static void Main(string[] args)
        {
            IAtCoderQuestion question = new QuestionE();    // 問題に合わせて書き換え
            var answers = question.Solve(Console.In);
            foreach (var answer in answers)
            {
                Console.WriteLine(answer);
            }
        }
    }
}

#region Base Classes

namespace AtCoderBeginnerContest153.Questions
{

    public interface IAtCoderQuestion
    {
        IEnumerable<object> Solve(string input);
        IEnumerable<object> Solve(TextReader inputStream);
    }

    public abstract class AtCoderQuestionBase : IAtCoderQuestion
    {
        public IEnumerable<object> Solve(string input)
        {
            var stream = new MemoryStream(Encoding.Unicode.GetBytes(input));
            var reader = new StreamReader(stream, Encoding.Unicode);

            return Solve(reader);
        }

        public abstract IEnumerable<object> Solve(TextReader inputStream);
    }

}

#endregion

#region Extensions

namespace AtCoderBeginnerContest153.Extensions
{
    internal static class TextReaderExtensions
    {
        internal static int ReadInt(this TextReader reader) => int.Parse(ReadString(reader));
        internal static long ReadLong(this TextReader reader) => long.Parse(ReadString(reader));
        internal static double ReadDouble(this TextReader reader) => double.Parse(ReadString(reader));
        internal static string ReadString(this TextReader reader) => reader.ReadLine();

        internal static int[] ReadIntArray(this TextReader reader, char separator = ' ') => ReadStringArray(reader, separator).Select(int.Parse).ToArray();
        internal static long[] ReadLongArray(this TextReader reader, char separator = ' ') => ReadStringArray(reader, separator).Select(long.Parse).ToArray();
        internal static double[] ReadDoubleArray(this TextReader reader, char separator = ' ') => ReadStringArray(reader, separator).Select(double.Parse).ToArray();
        internal static string[] ReadStringArray(this TextReader reader, char separator = ' ') => reader.ReadLine().Split(separator);
    }
}

#endregion

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