// Original C++ solution (slower):
#include <iostream>

#include <vector>

#include <algorithm>

#include <map>

#include <numeric>

#include <string>

#include <cstdio>

#include <cstring>

#include <queue>

#include <stack>

#include <set>

#include <cmath>

#include <bitset>



typedef long long ll;

typedef unsigned long long ull;

using namespace std;



#define FALSE printf("false\n");

#define TRUE printf("true\n");

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

#define rep(i,n) for(int i = 0;i < ((int)(n));++i)

#define pb push_back

#define mp make_pair

#define fi first

#define se second

#define UNIQUE(v) v.erase( unique(v.begin(), v.end()), v.end() );

#define test(a) cout<<"line:"<<__LINE__<<"["<<(#a)<<": "<<(a)<<"]"<<endl



const int INF = 1e9+7;

const ll INFL = 9*1e18;



// const int dx[4] = { 1, 0, -1, 0 };

// const int dy[4] = { 0, 1, 0, -1 };



// const int dx[8] = {1, 1, 0,-1,-1,-1, 0, 1};

// const int dy[8] = {0, 1, 1, 1, 0,-1,-1,-1};



#define SUM(vec) accumulate(all(vec),0LL) // 配列の中身を全部足す

template<typename T>void print(T&& x){cout<<x<<endl;}// 改行付き出力

ll inline digit(ll num){int tmp = 0;while(num){tmp++;num/=10;}return tmp;} // 桁数

template<typename T>inline T digitSum(T num){T sum = 0;while(num){sum+=num%10;num/=10;}return sum;} // 各桁の和

template<typename T>inline T gcd(T a,T b){if(b == 0)return a;return gcd(b,a%b);} // 最大公約数

template<typename T>inline T lcm(T a, T b){T g = gcd(a,b);return a/g*b;} // 最小公倍数

template<typename T>inline T power(T a,T b){T tmp=1;rep(i,b){tmp*=a;}return tmp;} // 累乗

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }

template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

int ctoi(char c){return c-'0';}



// TODO: write

int main() {   

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

  vector<int> a(n),b(n);

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

  vector<vector<int>> dp(n+10,vector<int>(h+10,INF));

  rep(i,n+10)dp[i][0] = 0;

  

  rep(i,n){

    rep(j,h+1){

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

      chmin(dp[i+1][j],dp[i+1][max(j-a[i],0)]+b[i]);

    }

  }



  print(dp[n][h]);

  return 0;

}




// Optimized solution to the same problem (faster):
#include <iostream>

#include <vector>

#include <algorithm>

#include <map>

#include <numeric>

#include <string>

#include <cstdio>

#include <cstring>

#include <queue>

#include <stack>

#include <set>

#include <cmath>

#include <bitset>



typedef long long ll;

typedef unsigned long long ull;

using namespace std;



#define FALSE printf("false\n");

#define TRUE printf("true\n");

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

#define rep(i,n) for(int (i) = 0;(i) < ((int)(n));++(i))

#define pb push_back

#define mp make_pair

#define fi first

#define se second

#define UNIQUE(v) v.erase( unique(v.begin(), v.end()), v.end() );

#define test(a) cout<<"line:"<<__LINE__<<"["<<(#a)<<": "<<(a)<<"]"<<endl



const int INF = 1e9+7;

const ll INFL = 9*1e18;



const int dx[4] = { 1, 0, -1, 0 };

const int dy[4] = { 0, 1, 0, -1 };



// const int dx[8] = {1, 1, 0,-1,-1,-1, 0, 1};

// const int dy[8] = {0, 1, 1, 1, 0,-1,-1,-1};



#define SUM(vec) accumulate(all(vec),0LL) // 配列の中身を全部足す

template<typename T>void print(T&& x){cout<<x<<endl;}// 改行付き出力

ll inline digit(ll num){int tmp = 0;while(num){tmp++;num/=10;}return tmp;} // 桁数

template<typename T>inline T digitSum(T num){T sum = 0;while(num){sum+=num%10;num/=10;}return sum;} // 各桁の和

template<typename T>inline T gcd(T a,T b){if(b == 0)return a;return gcd(b,a%b);} // 最大公約数

template<typename T>inline T lcm(T a, T b){T g = gcd(a,b);return a/g*b;} // 最小公倍数

template<typename T>inline T power(T a,T b){T tmp=1;rep(i,b){tmp*=a;}return tmp;} // 累乗

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }

template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

int ctoi(char c){return c-'0';}



// TODO: write

int main() {

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

  vector<pair<int,int>> a(n);rep(i,n)cin>>a[i].fi>>a[i].se;

  vector<vector<int>> dp(n+1,vector<int>(h+1,INF));

  

  rep(i,n)dp[i][0] = 0;

  rep(i,n){

    rep(j,h+1){

      chmin(dp[i][j],dp[max(i-1,0)][j]);

      chmin(dp[i][j],dp[i][max(j-a[i].fi,0)] + a[i].se);

    }

  }

  print(dp[n-1][h]);

  return 0;

}


// Fastest known solution for this problem: