#include <bits/stdc++.h>
#define INF 90000000
using namespace std;

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

int n, G, sum, dp[1001][100000];

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

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

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