#include <bits/stdc++.h>
#define INF 1000000
using namespace std;

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

int n, G, sum, L1[10000001], L2[10000001], sol = INF;

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

int GetCostMinim(int N, int g)
{
    if (N > 0 && g < G)
    {
        return min(GetCostMinim(N - 1, g), v[N].c + GetCostMinim(N - 1, g + v[N].e));
    }
    if (g < G)
    {
        return INF;
    }
    return 0;
}

void Read()
{
    fin >> n >> G;
    for (int i = 1; i <= G; ++i)
    {
        fin >> v[i].e >> v[i].c;
        sum += 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 = sum - v[i].e; j >= 0; --j)
        {
            L2[j] = min(L1[j], v[i].c + L1[j + v[i].e]);
            if (i == n)
            {
                if (L2[j] != 0)
                    sol = min(sol, L2[j]);
            }
        }
	for (int j = 0; j <= sum; ++j)
	     L1[j] = L2[j];
    }
    fout << sol;
}

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