import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.AbstractMap.SimpleEntry;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.PriorityQueue;
import java.util.Scanner;
import java.util.StringTokenizer;

class Main {
    static final int MOD = 1000000007;
    static final int INF = 1 << 30;

    Main() {
        Scanner sc = new Scanner(System.in);
        long ans = INF;
        int H = sc.nextInt();
        int N = sc.nextInt();
        ArrayList<Entry<Integer, Integer>> list = new ArrayList<Entry<Integer, Integer>>(N);
        for (int i = 0; i < N; i++) {
            int a = sc.nextInt();
            int b = sc.nextInt();
            list.add(new SimpleEntry<Integer, Integer>(b, a));
        }
        int[] dp = new int[H*2+1];
        dp[0]=0;
        Arrays.fill(dp, INF);
        for (int i = 1; i <= H*2; i++) {
            for (int k = 0; k < N; k++) {
                Entry<Integer, Integer> entry = list.get(k);
                if (i - entry.getValue() > 0) {
                    dp[i] = Math.min(dp[i - entry.getValue()] + entry.getKey(), dp[i]);
                } else {
                    dp[i] = Math.min(entry.getKey(), dp[i]);
                }
            }
        }
        for(int i=H;i<H*2;i++){
            ans = Math.min(dp[i],ans);
        }
        System.out.println(ans);
    }

    public static void main(String[] args) {
        new Main();
    }
}

class FastScanner {
    private BufferedReader reader = null;
    private StringTokenizer tokenizer = null;

    public FastScanner(InputStream in) {
        reader = new BufferedReader(new InputStreamReader(in));
        tokenizer = null;
    }

    public String next() {
        if (tokenizer == null || !tokenizer.hasMoreTokens()) {
            try {
                tokenizer = new StringTokenizer(reader.readLine());
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
        return tokenizer.nextToken();
    }

    public String nextLine() {
        if (tokenizer == null || !tokenizer.hasMoreTokens()) {
            try {
                return reader.readLine();
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }

        return tokenizer.nextToken("\n");
    }

    public long nextLong() {
        return Long.parseLong(next());
    }

    public int nextInt() {
        return Integer.parseInt(next());
    }

    public double nextDouble() {
        return Double.parseDouble(next());
    }

    public ArrayList<Integer> nextIntList(int n) {
        ArrayList<Integer> a = new ArrayList<Integer>(n);
        for (int i = 0; i < n; i++)
            a.add(nextInt());
        return a;
    }

    public ArrayList<Long> nextLongList(int n) {
        ArrayList<Long> a = new ArrayList<Long>(n);
        for (int i = 0; i < n; i++)
            a.add(nextLong());
        return a;
    }

    public int[] nextIntArray(int n) {
        int[] a = new int[n];
        for (int i = 0; i < n; i++)
            a[i] = nextInt();
        return a;
    }

    public long[] nextLongArray(int n) {
        long[] a = new long[n];
        for (int i = 0; i < n; i++)
            a[i] = nextLong();
        return a;
    }
}

Measured memory_bytes: 27408