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

using namespace std;

using lint = long long int;

using pint = pair<int, int>;

using plint = pair<lint, lint>;

struct fast_ios { fast_ios(){ cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_;

#define ALL(x) (x).begin(), (x).end()

#define SZ(x) ((lint)(x).size())

#define POW2(n) (1LL << (n))

#define FOR(i, begin, end) for(int i=(begin),i##_end_=(end);i<i##_end_;i++)

#define IFOR(i, begin, end) for(int i=(end)-1,i##_begin_=(begin);i>=i##_begin_;i--)

#define REP(i, n) FOR(i,0,n)

#define IREP(i, n) IFOR(i,0,n)

template<typename T> istream &operator>>(istream &is, vector<T> &vec){ for (auto &v : vec) is >> v; return is; }

template<typename T> ostream &operator<<(ostream &os, const vector<T> &vec){ os << "["; for (auto v : vec) os << v << ","; os << "]"; return os; }

template<typename T> ostream &operator<<(ostream &os, const deque<T> &vec){ os << "deq["; for (auto v : vec) os << v << ","; os << "]"; return os; }

template<typename T> ostream &operator<<(ostream &os, const set<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }

template<typename T> ostream &operator<<(ostream &os, const unordered_set<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }

template<typename T> ostream &operator<<(ostream &os, const multiset<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }

template<typename T> ostream &operator<<(ostream &os, const unordered_multiset<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }

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

template<typename TK, typename TV> ostream &operator<<(ostream &os, const map<TK, TV> &mp){ os << "{"; for (auto v : mp) os << v.first << "=>" << v.second << ","; os << "}"; return os; }

template<typename TK, typename TV> ostream &operator<<(ostream &os, const unordered_map<TK, TV> &mp){ os << "{"; for (auto v : mp) os << v.first << "=>" << v.second << ","; os << "}"; return os; }

template<typename T> void ndarray(vector<T> &vec, int len) { vec.resize(len); }

template<typename T, typename... Args> void ndarray(vector<T> &vec, int len, Args... args) { vec.resize(len); for (auto &v : vec) ndarray(v, args...); }

template<typename T> bool mmax(T &m, const T q) { if (m < q) {m = q; return true;} else return false; }

template<typename T> bool mmin(T &m, const T q) { if (q < m) {m = q; return true;} else return false; }

template<typename T1, typename T2> pair<T1, T2> operator+(const pair<T1, T2> &l, const pair<T1, T2> &r) { return make_pair(l.first + r.first, l.second + r.second); }

template<typename T1, typename T2> pair<T1, T2> operator-(const pair<T1, T2> &l, const pair<T1, T2> &r) { return make_pair(l.first - r.first, l.second - r.second); }

#define dbg(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ") " << __FILE__ << endl;

/*

#include <ext/pb_ds/assoc_container.hpp>

#include <ext/pb_ds/tree_policy.hpp>

#include <ext/pb_ds/tag_and_trait.hpp>

using namespace __gnu_pbds; // find_by_order(), order_of_key()

template<typename TK> using pbds_set = tree<TK, null_type, less<TK>, rb_tree_tag, tree_order_statistics_node_update>;

template<typename TK, typename TV> using pbds_map = tree<TK, TV, less<TK>, rb_tree_tag, tree_order_statistics_node_update>;

*/





int main()

{

    int H;

    cin >> H;

    lint N;

    cin >> N;

    vector<lint> A(N);

    vector<lint> B(N);

    REP(i, N){ cin >> A[i]; cin >> B[i]; }

    vector<lint> dp(100000, 1e9);

    dp[0] = 0;

    REP(k, N) {

        REP(i, H) if (i + A[k] <= dp.size()) mmin(dp[i + A[k]], dp[i] + B[k]);

    }

    IREP(i, dp.size() - 1) mmin(dp[i], dp[i + 1]);

    cout << dp[H] << endl;

}


// Faster C++ solution for the same problem (measured speedup: 1.2979628930464209x):
#include <bits/stdc++.h>

using namespace std;

#define FOR(i, begin, end) for(int i=(begin),i##_end_=(end);i<i##_end_;i++)

#define IFOR(i, begin, end) for(int i=(end)-1,i##_begin_=(begin);i>=i##_begin_;i--)

#define REP(i, n) FOR(i,0,n)

#define IREP(i, n) IFOR(i,0,n)

template<typename T> bool mmin(T &m, const T q) { if (q < m) {m = q; return true;} else return false; }





int main()

{

    int H, N;

    cin >> H >> N;

    vector<int> dp(100000, 1e9);

    dp[0] = 0;

    while (N--) {

        int A, B;

        cin >> A >> B;

        REP(i, H) mmin(dp[i + A], dp[i] + B);

    }

    IREP(i, dp.size() - 1) mmin(dp[i], dp[i + 1]);

    cout << dp[H] << endl;

}