using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;

namespace CsharpSpiral {
    partial class Program {
        //https://qiita.com/NotFounds/items/7b166af69a6f52a332de
        static void Main(string[] args) {
            var sw = new StreamWriter( Console.OpenStandardOutput() ) { AutoFlush = false };
            Console.SetOut( sw );
            new Program().Solve( new ConsoleInput( Console.In, ' ' ) );
            Console.Out.Flush();
        }
        public void Solve(ConsoleInput cin) {
            var input = cin.ReadIntArray(2);
            var H = input[0];var N = input[1];
            var A = new int[N];
            var B = new int[N];
            for (int i = 0; i < N; i++) {
                input = cin.ReadIntArray( 2 );
                A[i] = input[0];
                B[i] = input[1];
            }

            var Damage2Mana = new long[H+1];
            var Numbers = Enumerable.Range( 0, N );
            Damage2Mana[0] = 0;
            for (int j = 1; j < H+1; j++) {
                Damage2Mana[j] = Numbers.Select( i => (j - A[i] < 0 ? 0 : Damage2Mana[j - A[i]]) + B[i] ).Min();
            }
            Console.WriteLine(Damage2Mana[H]);
        }

        
    }

    static class ExtendClass {
        public static void Swap<T>(this T[] X, int i, int j) {
            T tmp = X[i];
            X[i] = X[j];
            X[j] = tmp;
        }
        public static string Join<T> (this T[] X, string separator = " ") => string.Join( separator, X);
        public static S[] Clone<S>(this S[] src) where S : struct {
            var res = new S[src.Length];
            Array.Copy( src, res, src.Length );
            return res;
        }
    }

    class ConsoleInput {
        private readonly TextReader _stream;
        private char _separator = ' ';
        private Queue<string> inputStream;
        public ConsoleInput(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: 13436