#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using P = pair<ll, ll>;
using Pld = pair<ld, ld>;
using Vec = vector<ll>;
using VecP = vector<P>;
using VecB = vector<bool>;
using VecC = vector<char>;
using VecD = vector<ld>;
using VecS = vector<string>;
template <class T>
using Vec2 = vector<vector<T>>;
#define REP(i, m, n) for(ll i = (m); i < (n); ++i)
#define REPN(i, m, n) for(ll i = (m); i <= (n); ++i)
#define REPR(i, m, n) for(ll i = (m)-1; i >= (n); --i)
#define REPNR(i, m, n) for(ll i = (m); i >= (n); --i)
#define rep(i, n) REP(i, 0, n)
#define repn(i, n) REPN(i, 1, n)
#define repr(i, n) REPR(i, n, 0)
#define repnr(i, n) REPNR(i, n, 1)
#define all(s) (s).begin(), (s).end()
#define pb push_back
#define fs first
#define sc second
template <class T1, class T2>
bool chmax(T1 &a, const T2 b){if(a < b){a = b; return true;} return false;}
template <class T1, class T2>
bool chmin(T1 &a, const T2 b){if(a > b){a = b; return true;} return false;}
ll pow2(const int n){return (1LL << n);}
void co() { cout << endl; }
template <class Head, class... Tail>
void co(Head&& head, Tail&&... tail) {
    cout << head << ' ';
    co(forward<Tail>(tail)...);
}
void ce() { cerr << endl; }
template <class Head, class... Tail>
void ce(Head&& head, Tail&&... tail) {
    cerr << head << ' ';
    ce(forward<Tail>(tail)...);
}
void sonic(){ios::sync_with_stdio(false); cin.tie(0);}
void setp(const int n){cout << fixed << setprecision(n);}
constexpr int INF = 1e9+1;
constexpr ll LINF = 1e18L+1;
constexpr ll MOD = 1e9L+7;
constexpr ll MOD_N = 998244353;
constexpr ld EPS = 1e-11;
const double PI = acos(-1);

template <int mod>
struct ModInt {
    int x;

    ModInt() : x(0) {}

    ModInt(int64_t y) : x(y >= 0 ? y % mod : (mod - (-y) % mod) % mod) {}

    ModInt &operator+=(const ModInt &p) {
        if((x += p.x) >= mod) x -= mod;
        return *this;
    }

    ModInt &operator-=(const ModInt &p) {
        if((x += mod - p.x) >= mod) x -= mod;
        return *this;
    }

    ModInt &operator*=(const ModInt &p) {
        x = (int) (1LL * x * p.x % mod);
        return *this;
    }

    ModInt &operator/=(const ModInt &p) {
        *this *= p.inverse();
        return *this;
    }

    ModInt &operator++() {
        if((++x) >= mod) x -= mod;
        return *this;
    }

    ModInt operator++(int) {
        ModInt tmp(*this);
        operator++();
        return tmp;
    }

    ModInt &operator--() {
        if((x += mod - 1) >= mod) x -= mod;
        return *this;
    }

    ModInt operator--(int) {
        ModInt tmp(*this);
        operator--();
        return tmp;
    }

    ModInt operator-() const { return ModInt(-x); }

    ModInt operator+(const ModInt &p) const { return ModInt(*this) += p; }

    ModInt operator-(const ModInt &p) const { return ModInt(*this) -= p; }

    ModInt operator*(const ModInt &p) const { return ModInt(*this) *= p; }

    ModInt operator/(const ModInt &p) const { return ModInt(*this) /= p; }

    bool operator==(const ModInt &p) const { return x == p.x; }

    bool operator!=(const ModInt &p) const { return x != p.x; }

    ModInt inverse() const {
        int a = x, b = mod, u = 1, v = 0, t;
        while(b > 0) {
            t = a / b;
            swap(a -= t * b, b);
            swap(u -= t * v, v);
        }
        return ModInt(u);
    }

    ModInt pow(int64_t n) const {
        ModInt res(1), mul(x);
        while(n > 0) {
            if(n & 1) res *= mul;
            mul *= mul;
            n >>= 1;
        }
        return res;
    }

    friend ostream &operator<<(ostream &os, const ModInt &p) {
        return os << p.x;
    }

    friend istream &operator>>(istream &is, ModInt &a) {
        int64_t t;
        is >> t;
        a = ModInt< mod >(t);
        return (is);
    }

    static int get_mod() { return mod; }
};
using Mint = ModInt<10000>;

int main(void){
    ll h, n;
    cin >> h >> n;
    Vec a(n), b(n);
    rep(i, n) cin >> a[i] >> b[i];

    Vec dp(h + 1, LINF);
    dp[0] = 0;
    rep(i, n){
        rep(j, h){
            chmin(dp[min(j + a[i], h)], dp[j] + b[i]);
        }
    }
    cout << dp[h] << endl;

    return 0;
}


Measured memory_bytes: 3700