#include <bits/stdc++.h>
#define INF 99000000
using namespace std;

ifstream fin("energii.in");
ofstream fout("energii.out");

int n, G, maxi, L1[21001], L2[21001], sol = INF;

struct Generator
{
    int e, c;
}v[1002];


void Read()
{
    fin >> n >> G;
    for (int i = 1; i <= G; ++i)
    {
        fin >> v[i].e >> v[i].c;
        maxi = max(maxi, v[i].e);
    }
}

void Solve()
{
    for (int j = 0; j < G; ++j)
    {
        L1[j] = INF;
    }
    for (int i = 1; i <= n; ++i)
    {
        for (int j = 0; j <= G + maxi; ++j)
        {
            L2[j] = min(L1[j], v[i].c + L1[j + v[i].e]);
        }
        for (int j = 0; j <= G + maxi; ++j)
        {
            L1[j] = L2[j];
        }
    }
    fout << L2[0] << " ";
}

int main()
{
    Read();
    Solve();
    fin.close();
    fout.close();
    return 0;
}