#include <bits/stdc++.h>

using namespace std;

#define DUMP(x) std::cerr << (#x) << " = " << (x) << "\n"
#define rep(i, n) for (int i = 0; i < (int)(n); ++i)
#define REP(i, k, n) for (int i = (k); i < (int)(n); ++i)
#define ALL(r) r.begin(), r.end()
#define YES cout << "YES" << endl
#define Yes cout << "Yes" << endl
#define NO cout << "NO" << endl
#define No cout << "No" << endl
#define IMP cout << "IMPOSSIBLE" << endl
#define Imp cout << "Impossible" << endl
#define imp cout << "impossible" << endl
#define M1 cout << "-1" << endl
#define pb push_back
#define eb emplace_back
#define fi first
#define se second

template <typename T>
ostream &operator<<(ostream &os, vector<T> &v)
{
    os << "{";
    rep(i, v.size()) os << v[i] << (i == (int)v.size() - 1 ? "" : ", ");
    os << "}";
    return os;
}
template <typename T>
T dup(T x, T y)
{
    return (x + y - 1) / y;
};
template <typename A, size_t N, typename T>
inline void arrayFill(A (&array)[N], const T &val) { std::fill((T *)array, (T *)(array + N), val); }
struct in
{
    const size_t n = 0;
    in() = default;
    in(size_t n) : n(n){};
    template <typename T>
    operator T()
    {
        T ret;
        cin >> ret;
        return ret;
    }
    template <typename T>
    operator vector<T>()
    {
        assert(n != 0);
        vector<T> ret(n);
        for (auto &x : ret)
            cin >> x;
        return ret;
    }
};

using ll = int64_t;
using vint = vector<int32_t>;
using vvint = vector<vint>;
using vll = vector<ll>;
using vvll = vector<vll>;
using vstr = vector<string>;
using pint = pair<int32_t, int32_t>;
using vpint = vector<pint>;
using pll = pair<ll, ll>;
using vpll = vector<pll>;
using setint = set<int32_t>;
using setstr = set<string>;
using qint = queue<int32_t>;
using qpint = queue<pint>;

constexpr std::int32_t INF = 1001001001;
constexpr std::int64_t LINF = 1001001001001001001;

template <class T>
inline bool chmax(T &a, T b)
{
    if (a < b)
    {
        a = b;
        return true;
    }
    return false;
}
template <class T>
inline bool chmin(T &a, T b)
{
    if (a > b)
    {
        a = b;
        return true;
    }
    return false;
}

struct Edge
{
    int to, cost;
};

using Graph = vector<vector<Edge>>;

void dijkstra(const Graph &g, vint &dist, int s)
{
    priority_queue<pint, vpint, greater<pint>> q;

    dist[s] = 0;
    q.emplace(0, s);

    while (!q.empty())
    {
        pint p = q.top();
        q.pop();
        int v = p.se;
        if (dist[v] < p.fi)
            continue;
        for (const auto e : g[v])
        {
            if (dist[e.to] > dist[v] + e.cost)
            {
                dist[e.to] = dist[v] + e.cost;
                q.emplace(dist[e.to], e.to);
            }
        }
    }
}

void Main()
{
    int h = in(), n = in();
    vint a(n), b(n);
    rep(i, n)
    {
        cin >> a[i] >> b[i];
    }

    Graph g(h + 10005);

    rep(i, n)
    {
        rep(j, h)
        {
            g[j].push_back({j + a[i], b[i]});
        }
    }

    vint dist(h + 10005, INF);

    dijkstra(g, dist, 0);

    int ans = INF;
    REP(i, h, h + 10003)
    {
        ans = min(ans, dist[i]);
    }
    cout << ans << endl;
}

signed main()
{
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    std::cout << std::fixed << std::setprecision(15);
    Main();
    return 0;
}


Measured memory_bytes: 86000