#include <bits/stdc++.h>
#define rep(i,n) for(int64_t i=0;i < (int64_t)(n);i++)
#define invrep(i,n) for(int64_t i=n-1;i >= 0L;i--)
#define positiverep(i,n) for(int64_t i=1;i <= (int64_t)(n);i++)
using namespace std;

//////全探索したいときに開けよ////////
vector<vector<int>> fspattern;
vector<int> fspattern_draft;
int fspcnt = 0;

void setfspattern_core(int floor,int number,int degree){
  if(floor==degree){
    fspattern.at(fspcnt) = fspattern_draft;
    fspcnt++;
  }else{
    rep(i,number){
      fspattern_draft.at(floor) = i;
      setfspattern_core(floor+1,number,degree);
    }
  }
}

void setfspattern(int number,int degree){
  int64_t array_num = 1;
  rep(i,degree){
    array_num *= number;
  }
  fspattern = vector<vector<int>>(array_num,vector<int>(degree));
  fspattern_draft = vector<int>(degree);
  setfspattern_core(0,number,degree);
}

//////nCrのmodを求めたいときに開けよ/////////
//int64_t univMod = 1000000007;
//int64_t factnum = 100000
//vector<int64_t> modfact(factnum);
//vector<int64_t> modinvfact(factnum);

/*void setmodfact(){
  for(int i=0;i<factnum;i++){
    if(i == 0){
      modfact.at(i) = 1;
    }else{
      modfact.at(i) = (modfact.at(i-1)*i)%univMod;
    }
  }
}

int64_t calcmodpower(int64_t a,int64_t n){
  int64_t res = 1;
  while(n != 0){
    if(n & 1){
      res = (res * a) % univMod;
    }
    a = (a*a) % univMod;
    n = n >> 1;
  }
  return res;
}

int64_t calcinverse(int64_t n){
	return calcmodpower(n,univMod-2);
}

void setmodinvfact(){
  for(int i=0;i<factnum;i++){
    if(i==0){
      modinvfact.at(i) = 1;
    }else{
      modinvfact.at(i) = calcmodpower(modfact.at(i),univMod-2);
    }
  }
}

int64_t calcmodcomb(int64_t n,int64_t r){
  return (((modfact.at(n)*modinvfact.at(r))%univMod)*modinvfact.at(n-r))%univMod;
}

int64_t calcmodpositive(int64_t n){
  return (n + ((abs(n)+univMod-1)/univMod)*univMod)%univMod;
}
  
    */


/*
int64_t calcGCD(int64_t a,int64_t b){
	int64_t p = a;
	int64_t q = b;
	int64_t c = a%b;
	while(c != 0){
		p = q;
		q = c;
		c = p%q;
	}
	return q;
}
*/

int main(){
  int64_t h,n;
  cin >> h >> n;
  vector<int64_t> a(n),b(n);
  rep(i,n){
    cin >> a.at(i) >> b.at(i);
  }
  int64_t infinity_ = 1000000000;
  vector<vector<int64_t>> DP(1500,vector<int64_t>(30000));
  rep(i,1500){
    rep(j,15000){
      DP.at(i).at(j) = infinity_;
    }
  }
  rep(j,h+1){
    if(j == 0){
      DP.at(0).at(j) = 0;
    }else{
      DP.at(0).at(j) = infinity_;
    }
  }
  
      
  
  rep(i,n){
    rep(j,h+10050){
        if(j-a.at(i)>=0){
          DP.at(i+1).at(j) = min(DP.at(i).at(j),DP.at(i+1).at(j-a.at(i))+b.at(i));
        }else{
          DP.at(i+1).at(j) = DP.at(i).at(j);
        }
    }
  }
      /*rep(k,n+1){
        rep(l,h+1){
          if(DP.at(k).at(l) == 500){
            cout << '-';
          }else{
            cout << DP.at(k).at(l);
          }
        }
        cout << endl;
      }
      cout << "#####" << endl;
    }*/
  int64_t minmagic = infinity_;
  for(int i = h;i < 15000;i++){
    minmagic = min(minmagic,DP.at(n).at(i));
  }
  cout << minmagic << endl;
  /*rep(k,n+1){
    rep(l,h+1+10){
      if(DP.at(k).at(l) == 500){
        cout << '-';
      }else{
         cout << DP.at(k).at(l);
      }
    }
    cout << endl;
  }*/
 
}

Measured memory_bytes: 356372