#include <bits/stdc++.h>
using namespace std;
#define rep(i, a, b) for (int (i) = (a); (i) < (b); ++(i))
#define per(i, a, b) for (int (i) = (a); (i) >= (b); --(i))
#define pb push_back
#define mp make_pair
#define mt make_tuple
#define eb emplace_back
#define ff first
#define ss second
#define sz(x) ((int) x.size())
#define rd(type, ...) type __VA_ARGS__; sc(__VA_ARGS__)
#define rda(a, n) rep(i, 0, n) cin >> a[i];
#define rdaa(a, n, m) rep(i, 0, n) rep(j, 0, m) cin >> a[i][j];
#define rdv(type, v, n) vector<type> v(n); rep(__ii, 0, n) cin >> v[__ii]
#define rdm(type, v, h, w) vector<vector<type>> v(h, vector<type>(w)); rep(__ii, 0, h) rep(__jj, 0, w) cin >> v[__ii][__jj]
#define rdv2(type, n, ...)std::vector<type> __VA_ARGS__;MACRO_rdv2_Init(n, __VA_ARGS__); for(int w_=0; w_<n; ++w_){MACRO_rdv2_Scan(w_, __VA_ARGS__);}
#define dbg(...) cerr << "[" << #__VA_ARGS__ << "] : ", debug_out(__VA_ARGS__)
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
typedef long long ll;
typedef long double ld;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef pair<int, int> pii;
typedef vector<pii> vpii;
void solve();
signed main() {ios::sync_with_stdio(false); cin.tie(0);
  cout << fixed; cout.precision(20); solve(); return 0;}
template<typename T> void chmin(T &a, T b) {if (a > b) a = b;}
template<typename T> void chmax(T &a, T b) {if (a < b) a = b;}
template<typename T> void MACRO_rdv2_Init(int n, T& t) { t.resize(n); }
template<typename First, typename... Rest> void MACRO_rdv2_Init(int n, First& first, Rest& ...rest) { first.resize(n); MACRO_rdv2_Init(n, rest...); }
template<typename T> void MACRO_rdv2_Scan(int p, T& t) { std::cin >> t[p]; }
template<typename First, typename... Rest> void MACRO_rdv2_Scan(int p, First& first, Rest& ...rest) { std::cin >> first[p]; MACRO_rdv2_Scan(p, rest...); }
template<typename T> void wrv(const vector<T> &v) {rep(__ii, 0, sz(v)) {if (__ii) cout << ' '; cout << v[__ii];} cout << '\n';} 
template<typename T> void wrm(const vector<vector<T>> &v) {rep(__ii, 0, sz(v)) {rep(__jj, 0, v[__ii].size()) {if (__jj) cout << ' '; cout << v[__ii][__jj];} cout << '\n';}}
template<typename T> void sc(T& x) {cin >> x;}
template<typename Head, typename... Tail> void sc(Head& head, Tail&... tail) {cin >> head; sc(tail...);}
template<typename T> void wr(const T& x) {cout << x << '\n';}
template<typename Head, typename... Tail> void wr(const Head& head, const Tail&... tail) {cout << head << ' '; wr(tail...);}
template<typename T> void wrf(const T& x) {cout << x << endl;}
template<typename Head, typename... Tail> void wrf(const Head& head, const Tail&... tail) {cout << head << ' '; wrf(tail...);}
template<typename T> void debug_out(const T& x) {cerr << x << '\n';}
template<typename Head, typename... Tail> void debug_out(const Head& head, const Tail&... tail) {cerr << head << ' '; debug_out(tail...);}
template<typename... T> void err(const T&... cod) {wr(cod...); exit(0);}
#define int ll

const int H = 1e4 + 5;
const int N = 1e3 + 5;

int h, n;
int dp[N][H];
int a[N], b[N];

void solve() {
  cin >> h >> n;
  rep(i, 1, n + 1) cin >> a[i] >> b[i];
  rep(i, 0, N) rep(j, 0, H) dp[i][j] = 9e18;
  dp[0][0] = 0;
  rep(i, 1, n + 1) rep(j, 0, h + 1) {
    int z;
    if (j - a[i] >= 0) z = dp[i][j - a[i]];
    else z = 0;
    chmin(dp[i][j], dp[i - 1][j]);
    chmin(dp[i][j], z + b[i]);
  }
  wr(dp[n][h]);
}

Measured memory_bytes: 78848