using System;
using System.Text;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
using static System.Console;
using static System.Math;

namespace AtCoder
{
    class Program
    {
        static void Main(string[] args)
        {
            new Program().Solve(new ConsoleInput(Console.In, ' '));
#if DEBUG
            ReadLine();
#endif
        }

        void Solve(ConsoleInput cin)
        {
            int h = cin.ReadInt;
            int n = cin.ReadInt;

            List<Magic> magics = new List<Magic>();
            for (int i = 0; i < n; i++)
            {
                Magic magic = new Magic(cin.ReadInt, cin.ReadInt);
                magics.Add(magic);
            }

            magics = magics.OrderBy(x => x.damage).ToList<Magic>();
            long[] dp = new long[h + magics.Select(x => x.damage).Max()];
            dp[0] = 0;
            for (int i = 1; i < dp.Length; i++) dp[i] = int.MaxValue;

            for (int i = 1; i < magics.First().damage; i++)
            {
                dp[i] = magics.First().mp;
            }

            int limit = dp.Length;
            for (int i = magics.First().damage; i < limit; i++)
            {
                foreach (Magic magic in magics)
                {
                    if (i - magic.damage < 0)
                    {
                        break;
                    }

                    if (dp[i - magic.damage] + magic.mp < dp[i])
                    {
                        dp[i] = dp[i - magic.damage] + magic.mp;
                    }
                }
            }

            Console.WriteLine(dp.Skip(h).Min());
        }

        class Magic
        {
            public int damage { get; set; }
            public int mp { get; set; }

            public Magic(int damage, int mp)
            {
                this.damage = damage;
                this.mp = mp;
            }
        }

        class ConsoleInput
        {
            private readonly System.IO.TextReader _stream;
            private char _separator = ' ';
            private Queue<string> inputStream;

            public ConsoleInput(System.IO.TextReader stream, char separator = ' ')
            {
                this._separator = separator;
                this._stream = stream;
                inputStream = new Queue<string>();
            }

            public string Read
            {
                get
                {
                    if (inputStream.Count != 0) return inputStream.Dequeue();
                    string[] tmp = _stream.ReadLine().Split(_separator);
                    for (int i = 0; i < tmp.Length; ++i)
                        inputStream.Enqueue(tmp[i]);
                    return inputStream.Dequeue();
                }
            }

            public string ReadLine { get { return _stream.ReadLine(); } }
            public int ReadInt { get { return int.Parse(Read); } }
            public long ReadLong { get { return long.Parse(Read); } }
            public double ReadDouble { get { return double.Parse(Read); } }
            public string[] ReadStrArray(long N) { var ret = new string[N]; for (long i = 0; i < N; ++i) ret[i] = Read; return ret; }
            public int[] ReadIntArray(long N) { var ret = new int[N]; for (long i = 0; i < N; ++i) ret[i] = ReadInt; return ret; }
            public long[] ReadLongArray(long N) { var ret = new long[N]; for (long i = 0; i < N; ++i) ret[i] = ReadLong; return ret; }
        }
    }
}

Measured memory_bytes: 13692