#include <algorithm>
#include <iostream>
#include <fstream>
#include <sstream>
#include <bitset>
#include <vector>
#include <deque>
#include <queue>
#include <stack>
#include <list>
#include <map>
#include <set>
#include <cmath>
#include <limits>
#include <numeric>
#include <iomanip>
#include <cstdlib>
#include <iterator>
#include <functional>
#include <unordered_map>
#include <unordered_set>

using namespace std;

typedef unsigned                    ui;
typedef int                         si;
typedef long                        sl;
typedef long long                   ll;
typedef unsigned long long          ull;

// ----------------

template <typename A, typename B>
string to_string(pair<A, B> p);

template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p);

template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p);

string to_string(const string& s) {
  return '"' + s + '"';
}

string to_string(const char* s) {
  return to_string((string) s);
}

string to_string(bool b) {
  return (b ? "true" : "false");
}

string to_string(vector<bool> v) {
  bool first = true;
  string res = "{";
  for (int i = 0; i < static_cast<int>(v.size()); i++) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(v[i]);
  }
  res += "}";
  return res;
}

template <size_t N>
string to_string(bitset<N> v) {
  string res = "";
  for (size_t i = 0; i < N; i++) {
    res += static_cast<char>('0' + v[i]);
  }
  return res;
}

template <typename A>
string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto &x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}

template <typename A, typename B>
string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}

template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ")";
}

template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ", " + to_string(get<3>(p)) + ")";
}

void debug_out() { cerr << endl; }

template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}

#ifdef LOCAL
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define debug(...) 42
#endif

// ----------------

const ll inf = 1e18;

int main(int argc, char *argv[])
{
    std::ios_base::sync_with_stdio(false);

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

    vector<ll> d(n, 0);
    vector<ll> c(n, 0);
    for (int i = 0; i < n; ++i) {
        cin >> d[i] >> c[i];
    }

    vector<ll> dp(h + 1, inf);
    dp[h] = 0;
    for (int i = h; i >= 0; --i) {
        if (dp[i] == inf) {
            continue;
        }
        for (int j = 0; j < n; ++j) {
            ll next = max(i - d[j], 0ll);
            dp[next] = min(dp[next], dp[i] + c[j]);
        }
    }

    cout << dp[0] << endl;

    return 0;
}


Measured memory_bytes: 384