// Slower C++ solution:
#include <bits/stdc++.h>

using namespace std;

typedef long long ll;



template<class T> inline bool chmin(T& a, T b) {

  if (a > b) { a = b; return 1; }

  return 0;

}



const ll INF = 1LL << 60;



int main()

{

  ll H; cin >> H;

  ll N; cin >> N;

  vector<ll> A(N);

  vector<ll> B(N);

  for (int i=0; i<N; i++){

    cin >> A[i];

    cin >> B[i];

  }

  vector<vector<ll>> dp(N+1, vector<ll>(H+10, INF));

  for (int i=0; i<N+1; i++) {

    dp[i][0] = 0;

  }

  for (int i=0; i<N; i++) {

    for (int j=1; j<H+1; j++) {

      dp[i+1][j] = min(dp[i][j] , dp[i+1][max(0LL, j-A[i])] + B[i]);

    }

  }

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



  return 0;

}


// Faster C++ solution for the same problem (measured speedup: 2.2455488358364146x):
#include <bits/stdc++.h>

using namespace std;

#define rep(i, a) for (int i = 0; i < (a); i++)

#define sz(x) (int)(x).size()

#define pcnt __builtin_popcountll

typedef long long ll;

template<typename T>istream& operator>>(istream&i,vector<T>&v){rep(j,sz(v))i>>v[j];return i;}

template<typename T>string join(const vector<T>&v){stringstream s;rep(i,sz(v))s<<' '<<v[i];return s.str().substr(1);}

template<typename T>ostream& operator<<(ostream&o,const vector<T>&v){if(sz(v))o<<join(v);return o;}

template<typename T1,typename T2>istream& operator>>(istream&i,pair<T1,T2>&v){return i>>v.first>>v.second;}

template<typename T1,typename T2>ostream& operator<<(ostream&o,const pair<T1,T2>&v){return o<<v.first<<","<<v.second;}

template<typename T>bool mins(T& x,const T&y){if(x>y){x=y;return true;}else return false;}

template<typename T>bool maxs(T& x,const T&y){if(x<y){x=y;return true;}else return false;}

template<typename T>ll suma(const vector<T>&a){ll res(0);for(auto&&x:a)res+=x;return res;}



#ifdef _DEBUG

inline void dump() { cerr << endl; }

template <typename Head> void dump(Head &&head) {

  cerr << head;

  dump();

}

template <typename Head, typename... Tail>

void dump(Head &&head, Tail &&... tail) {

  cerr << head << ", ";

  dump(forward<Tail>(tail)...);

}

#define dbg(...)                                                               \

  do {                                                                         \

    cerr << __LINE__ << ":\t" << #__VA_ARGS__ << " = ";                        \

    dump(__VA_ARGS__);                                                         \

  } while (false)

#else

#define dump(...)

#define dbg(...)

#endif



template <typename T> struct edge {

  int src, to;

  T cost;

  edge(int to, T cost) : src(-1), to(to), cost(cost) {}

  edge(int src, int to, T cost) : src(src), to(to), cost(cost) {}

  edge &operator=(const int &x) {

    to = x;

    return *this;

  }

  operator int() const { return to; }

};

template <typename T> using Edges = vector<edge<T>>;

template <typename T> using WeightedGraph = vector<Edges<T>>;

using UnWeightedGraph = vector<vector<int>>;

template <typename T> using Matrix = vector<vector<T>>;



const ll LINF = 1LL << 60;

const int INF = 1001001001;



/////////////////////////////////////////////////////////////////////



int main() {

  ll h,n; cin>>h>>n;

  vector<ll> a(n);

  vector<ll> b(n);

  rep(i, n) cin>>a[i]>>b[i];



  vector<ll> dp(h+1, LINF);

  dp[0] = 0;

  for (int i=0; i<n; i++) {

    for (int j=0; j<=h; j++) {

      dp[j] = min(dp[j], dp[max(0LL, j-a[i])] + b[i]);

    }

  }

  cout << dp[h] << endl;



  return 0;

}