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

using namespace std;

using ll = long long;

using ld = long double;

using VI = vector<int>;

using VL = vector<ll>;

template<class T> using PQ = priority_queue<T, vector<T>, greater<T>>;

#define FOR(i,a,n) for(int (i)=(a);(i)<(n);++(i))

#define eFOR(i,a,n) for(int (i)=(a);(i)<=(n);++(i))

#define rFOR(i,a,n) for(int (i)=(n)-1;(i)>=(a);--(i))

#define erFOR(i,a,n) for(int (i)=(n);(i)>=(a);--(i))

#define each(i, a) for(auto &i : a)

#define SORT(i) sort((i).begin(),(i).end())

#define rSORT(i,a) sort((i).begin(),(i).end(),(a))

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

#define out(y,x) ((y) < 0 || h <= (y) || (x) < 0 || w <= (x))

#define line cout << "------------------------\n" 

#define ENDL(i,n) ((i) == (n) - 1 ? "\n" : " ")

#define stop system("pause") //comment out this on AOJ.

constexpr ll INF = 1000000000;

constexpr ll LLINF = 1LL << 60;

constexpr ll mod = 1000000007;

constexpr ll MOD = 998244353;

constexpr ld eps = 1e-10; //1e-9?

constexpr ld pi = 3.1415926535897932;

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; }

inline void init() { cin.tie(nullptr); cout.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(15); }

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

template<class T, class U>inline istream& operator>>(istream& is, pair<T, U>& p) { is >> p.first >> p.second; return is; }

template<class T>inline vector<T> vec(size_t a) { return vector<T>(a); }

template<class T>inline vector<T> defvec(T def, size_t a) { return vector<T>(a, def); }

template<class T, class... Ts>inline auto vec(size_t a, Ts... ts) { return vector<decltype(vec<T>(ts...))>(a, vec<T>(ts...)); }

template<class T, class... Ts>inline auto defvec(T def, size_t a, Ts... ts) { return vector<decltype(defvec<T>(def, ts...))>(a, defvec<T>(def, ts...)); }



int main() {

    init();



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

    VL a(n), b(n);

    FOR(i, 0, n)cin >> a[i] >> b[i];



    auto dp = defvec<ll>(LLINF, n + 1, h + 1);

    dp[0][0] = 0;

    FOR(i, 0, n)eFOR(j, 0, h) {

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

        chmin(dp[i + 1][min(h, j + a[i])], dp[i + 1][j] + b[i]);

    }



    cout << dp[n][h] << "\n";

}


// Faster C++ solution for the same problem (measured speedup: 2.1490519750948245x):
#include <bits/stdc++.h>

using namespace std;

using ll = long long;

using ld = long double;

using VI = vector<int>;

using VL = vector<ll>;

using VS = vector<string>;

template<class T> using PQ = priority_queue<T, vector<T>, greater<T>>;

#define FOR(i,a,n) for(int (i)=(a);(i)<(n);++(i))

#define eFOR(i,a,n) for(int (i)=(a);(i)<=(n);++(i))

#define rFOR(i,a,n) for(int (i)=(n)-1;(i)>=(a);--(i))

#define erFOR(i,a,n) for(int (i)=(n);(i)>=(a);--(i))

#define each(i, a) for(auto &i : a)

#define SORT(i) sort((i).begin(),(i).end())

#define rSORT(i,a) sort((i).begin(),(i).end(),(a))

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

#define out(y,x) ((y) < 0 || h <= (y) || (x) < 0 || w <= (x))

#define line cout << "-----------------------------\n" 

#define ENDL(i,n) ((i) == (n) - 1 ? "\n" : " ")

#define stop system("pause")

constexpr ll INF = 1000000000;

constexpr ll LLINF = 1LL << 60;

constexpr ll mod = 1000000007;

constexpr ll MOD = 998244353;

constexpr ld eps = 1e-10;

constexpr ld pi = 3.1415926535897932;

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; }

inline void init() { cin.tie(nullptr); cout.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(15); }

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

template<class T>inline istream& operator>>(istream& is, deque<T>& v) { for (auto& elemnt : v)is >> elemnt; return is; }

template<class T, class U>inline istream& operator>>(istream& is, pair<T, U>& p) { is >> p.first >> p.second; return is; }

template<class T>inline vector<T> vec(size_t a) { return vector<T>(a); }

template<class T>inline vector<T> defvec(T def, size_t a) { return vector<T>(a, def); }

template<class T, class... Ts>inline auto vec(size_t a, Ts... ts) { return vector<decltype(vec<T>(ts...))>(a, vec<T>(ts...)); }

template<class T, class... Ts>inline auto defvec(T def, size_t a, Ts... ts) { return vector<decltype(defvec<T>(def, ts...))>(a, defvec<T>(def, ts...)); }



int main() {

    init();



    int h, n; cin >> h >> n;

    VI a(n), b(n);

    FOR(i, 0, n)cin >> a[i] >> b[i];



    VI dp(h + 1, INF);

    dp[0] = 0;

    FOR(i, 0, h)FOR(j, 0, n) {

        chmin(dp[min(i + a[j], h)], dp[i] + b[j]);

    }



    cout << dp[h] << "\n";

}