// Original C++ solution (slower):
// https://atcoder.jp/contests/abc153/tasks/abc153_e



#include "algorithm"

#include "bitset"

#include "cmath"

#include "functional"

#include "iomanip"

#include "iostream"

#include "map"

#include "numeric"

#include "queue"

#include "set"

#include "string"

#include "vector"

#define rep(i, to) for (ll i = 0; i < (to); ++i)

#define rep1(i, to) for (ll i = 1; i <= (to); ++i)

#define repf(i, from, to) for (ll i = from; i < (to); ++i)

#define repr(i, from) for (ll i = from - 1; i >= 0; --i)

#define all(vec) vec.begin(), vec.end()

#define unless(cond) if (!(cond))

#define fi first

#define se second

using namespace std;

typedef long long ll;

typedef long double ld;

template <typename T>

using V = vector<T>;

using VL = V<ll>;

using VVL = V<VL>;

template <typename T, typename U>

using P = pair<T, U>;

using PL = P<ll, ll>;

using VPL = V<PL>;

template <typename T>

inline bool chmax(T& a, T b);

template <typename T>

inline bool chmin(T& a, T b);

void print_ints(vector<ll> v);

template <typename T>

void drop(T a);



const ll INF = 1e18;



void solve() {

  ll H, N;

  cin >> H >> N;



  struct Mg {

    ll h, m;

  };



  V<Mg> mgs(N);



  rep(i, N) {

    ll h, m;

    cin >> h >> m;



    mgs[i] = {h, m};

  }



  // dp[i][h] // i 番目の魔法までで h 減らすのに必要な m

  VVL dp(N + 1, VL(H + 1, INF));

  dp[0][0] = 0;



  rep(i, N) rep(h, H + 1) {

    auto mg = mgs[i];

    chmin(dp[i + 1][h], dp[i][h]);

    chmin(dp[i + 1][min(H, h + mg.h)], dp[i + 1][h] + mg.m);

    chmin(dp[i + 1][min(H, h + mg.h)], dp[i][h] + mg.m);

  }



  cout << dp[N][H] << endl;

}



struct exit_exception : public std::exception {

  const char* what() const throw() { return "Exited"; }

};



#ifndef TEST

int main() {

  cin.tie(0);

  ios::sync_with_stdio(false);



  try {

    solve();

  } catch (exit_exception& e) {

  }



  return 0;

}

#endif



template <typename T>

inline bool chmax(T& a, T b) {

  if (a < b) {

    a = b;

    return 1;

  }

  return 0;

}



template <typename T>

inline bool chmin(T& a, T b) {

  if (a > b) {

    a = b;

    return 1;

  }

  return 0;

}



void print_ints(vector<ll> v) {

  rep(i, v.size()) {

    if (i > 0) {

      cout << " ";

    }



    cout << v[i];

  }



  cout << endl;

}



template <typename T>

void drop(T res) {

  cout << res << endl;

  throw exit_exception();

}


// Optimized solution to the same problem (faster):
// https://atcoder.jp/contests/abc153/tasks/abc153_e



#include "algorithm"

#include "bitset"

#include "cmath"

#include "functional"

#include "iomanip"

#include "iostream"

#include "map"

#include "numeric"

#include "queue"

#include "set"

#include "string"

#include "vector"

#define rep(i, to) for (ll i = 0; i < (to); ++i)

#define rep1(i, to) for (ll i = 1; i <= (to); ++i)

#define repf(i, from, to) for (ll i = from; i < (to); ++i)

#define repr(i, from) for (ll i = from - 1; i >= 0; --i)

#define all(vec) vec.begin(), vec.end()

#define unless(cond) if (!(cond))

#define fi first

#define se second

using namespace std;

typedef long long ll;

typedef long double ld;

template <typename T>

using V = vector<T>;

using VL = V<ll>;

using VVL = V<VL>;

template <typename T, typename U>

using P = pair<T, U>;

using PL = P<ll, ll>;

using VPL = V<PL>;

template <typename T>

inline bool chmax(T& a, T b);

template <typename T>

inline bool chmin(T& a, T b);

void print_ints(vector<ll> v);

template <typename T>

void drop(T a);



const ll INF = 1e18;



void solve() {

  ll H, N;

  cin >> H >> N;



  struct Mg {

    ll h, m;

  };



  V<Mg> mgs(N);



  rep(i, N) {

    ll h, m;

    cin >> h >> m;



    mgs[i] = {h, m};

  }



  // dp[i][h] // i 番目の魔法までで h 減らすのに必要な m

  VVL dp(N + 1, VL(H + 1, INF));

  dp[0][0] = 0;



  // 同じ要素ありのナップサック

  rep(i, N) rep(h, H + 1) {

    auto mg = mgs[i];

    chmin(dp[i + 1][h], dp[i][h]);

    chmin(dp[i + 1][min(H, h + mg.h)], dp[i + 1][h] + mg.m);

  }



  cout << dp[N][H] << endl;

}



void solve2() {

  ll H, N;

  cin >> H >> N;



  struct Mg {

    ll h, m;

  };



  V<Mg> mgs(N);



  rep(i, N) {

    ll h, m;

    cin >> h >> m;



    mgs[i] = {h, m};

  }



  VL dp(H + 1, INF);

  dp[0] = 0;



  rep(i, N) rep(h, H + 1) {

    auto mg = mgs[i];

    chmin(dp[min(H, h + mg.h)], dp[h] + mg.m);

  }



  cout << dp[H] << endl;

}



struct exit_exception : public std::exception {

  const char* what() const throw() { return "Exited"; }

};



#ifndef TEST

int main() {

  cin.tie(0);

  ios::sync_with_stdio(false);



  try {

    solve2();

  } catch (exit_exception& e) {

  }



  return 0;

}

#endif



template <typename T>

inline bool chmax(T& a, T b) {

  if (a < b) {

    a = b;

    return 1;

  }

  return 0;

}



template <typename T>

inline bool chmin(T& a, T b) {

  if (a > b) {

    a = b;

    return 1;

  }

  return 0;

}



void print_ints(vector<ll> v) {

  rep(i, v.size()) {

    if (i > 0) {

      cout << " ";

    }



    cout << v[i];

  }



  cout << endl;

}



template <typename T>

void drop(T res) {

  cout << res << endl;

  throw exit_exception();

}


// Fastest known solution for this problem: