// Slower C++ solution:
//include

//------------------------------------------

#include <bits/stdc++.h>

using namespace std;



//typedef

//------------------------------------------

using LL = int64_t;

using VL = vector<LL>;

using VVL = vector<VL>;

using VS = vector<string>;

using PLL = pair<LL, LL>;



//container util

//------------------------------------------

#define whole(f,x,...) ([&](decltype((x)) whole) { return (f)(begin(whole), end(whole), ## __VA_ARGS__); })(x)

#define rwhole(f,x,...) ([&](decltype((x)) whole) { return (f)(rbegin(whole), rend(whole), ## __VA_ARGS__); })(x)

#define EACH(i,c) for(decltype((c).begin()) i=(c).begin(); i!=(c).end(); ++i)

#define EXIST(s,e) ((s).find(e)!=(s).end())

#define SORT(c) whole(sort, c)

#define RSORT(c) rwhole(sort, c)



//constant

//--------------------------------------------

constexpr double EPS = 1e-10;

constexpr double PI  = M_PI;

constexpr int MOD = 1000000007;



// grid

//--------------------------------------------

VL dx = {0, 1, 0, -1};

VL dy = {1, 0, -1, 0};

VL dx2 = {-1, 0, 1, -1, 1, -1, 0, 1};

VL dy2 = {-1, -1, -1, 0, 0, 1, 1, 1};



//debug

//--------------------------------------------

#define dump(x)  cerr << #x << " = " << (x) << endl;

#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;



//IO accelerate

//--------------------------------------------

struct InitIO {

    InitIO() {

        cin.tie(nullptr);

        ios_base::sync_with_stdio(false);

        cout << fixed << setprecision(30);

    }

} init_io;



//template

//--------------------------------------------

// declaretion

template<typename T> istream& operator >>(istream& is, vector<T>& vec);

template<typename T1, typename T2> ostream& operator <<(ostream& os, const pair<T1, T2>& p);

template<typename T> ostream& operator <<(ostream& os, const vector<T>& vec);

template<typename T> ostream& operator <<(ostream& os, const vector<vector<T>>& vv);

template<typename T> vector<T> make_v(size_t a);

template<typename T,typename... Ts> auto make_v(size_t a,Ts... ts);

template<typename T,typename V> typename enable_if<is_class<T>::value==0>::type fill_v(T &t,const V &v);

template<typename T,typename V> typename enable_if<is_class<T>::value!=0>::type fill_v(T &t,const V &v);



// implementation

template<typename T>

istream& operator >>(istream& is, vector<T>& vec) {

	for(T& x: vec) is >> x;

	return is;

}

template<typename T1, typename T2>

ostream& operator <<(ostream& os, const pair<T1, T2>& p) {

	os << p.first << "," << p.second;

	return os;

}

template<typename T>

ostream& operator <<(ostream& os, const vector<T>& vec) {

	for(int i=0; i<vec.size(); i++){

		os << vec[i] << ( i+1 == vec.size() ? "" : "\t" );

	}

	return os;

}

template<typename T>

ostream& operator <<(ostream& s, const vector<vector<T>>& vv) {

	for (int i = 0; i < vv.size(); ++i) {

		s << vv[i] << endl;

	}

	return s;

}



// 多重vector

// auto dp=make_v<int>(4,h,w) みたいに使える

template<typename T>

vector<T> make_v(size_t a){return vector<T>(a);}



template<typename T,typename... Ts>

auto make_v(size_t a,Ts... ts){

	return vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...));

}



// 多重vectorのためのfill

// fill_v(dp,0) みたいに使える

template<typename T,typename V>

typename enable_if<is_class<T>::value==0>::type

fill_v(T &t,const V &v){t=v;}



template<typename T,typename V>

typename enable_if<is_class<T>::value!=0>::type

fill_v(T &t,const V &v){

	for(auto &e:t) fill_v(e,v);

}



template<class T,class U> void chmax(T&a,U b){if(a<b)a=b;}

template<class T,class U> void chmin(T&a,U b){if(b<a)a=b;}

template<typename T> T gcd(T a, T b) { return b?gcd(b,a%b):a;}

template<typename T> T lcm(T a, T b) { return a/gcd(a,b)*b;}



//main code



int main(int argc, char *argv[])

{

	LL h,n;

	cin >> h >> n;

	VL a(n), b(n);

	for (int i = 0; i < n; i++) {

		cin >> a[i] >> b[i];

	}

	VVL dp(n+1, VL(h+1,INT32_MAX));

	for (int i = 0; i < n+1; i++) {

		dp[i][0] = 0;

	}

	for (int i = 1; i <= n; i++) {

		for (int j = 0; j < min(a[i-1], h+1); j++) {

			dp[i][j] = dp[i-1][j];

		}

		for (int j = a[i-1]; j <= h; j++) {

			dp[i][j] = min(dp[i-1][j],min(dp[i-1][j-a[i-1]]+b[i-1], dp[i][j-a[i-1]] + b[i-1]));

		}

		for (int j = max(LL(h+1), a[i-1]); j < h + a[i-1]; j++) {

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

		}

	}

	cout << dp[n][h] << endl;

	return 0;

}




// Faster C++ solution for the same problem (measured speedup: 2.1468271374533776x):
//include

//------------------------------------------

#include <bits/stdc++.h>

using namespace std;



//typedef

//------------------------------------------

using LL = int64_t;

using VL = vector<LL>;

using VVL = vector<VL>;

using VS = vector<string>;

using PLL = pair<LL, LL>;



//container util

//------------------------------------------

#define whole(f,x,...) ([&](decltype((x)) whole) { return (f)(begin(whole), end(whole), ## __VA_ARGS__); })(x)

#define rwhole(f,x,...) ([&](decltype((x)) whole) { return (f)(rbegin(whole), rend(whole), ## __VA_ARGS__); })(x)

#define EACH(i,c) for(decltype((c).begin()) i=(c).begin(); i!=(c).end(); ++i)

#define EXIST(s,e) ((s).find(e)!=(s).end())

#define SORT(c) whole(sort, c)

#define RSORT(c) rwhole(sort, c)



//constant

//--------------------------------------------

constexpr double EPS = 1e-10;

constexpr double PI  = M_PI;

constexpr int MOD = 1000000007;



// grid

//--------------------------------------------

VL dx = {0, 1, 0, -1};

VL dy = {1, 0, -1, 0};

VL dx2 = {-1, 0, 1, -1, 1, -1, 0, 1};

VL dy2 = {-1, -1, -1, 0, 0, 1, 1, 1};



//debug

//--------------------------------------------

#define dump(x)  cerr << #x << " = " << (x) << endl;

#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;



//IO accelerate

//--------------------------------------------

struct InitIO {

    InitIO() {

        cin.tie(nullptr);

        ios_base::sync_with_stdio(false);

        cout << fixed << setprecision(30);

    }

} init_io;



//template

//--------------------------------------------

// declaretion

template<typename T> istream& operator >>(istream& is, vector<T>& vec);

template<typename T1, typename T2> ostream& operator <<(ostream& os, const pair<T1, T2>& p);

template<typename T> ostream& operator <<(ostream& os, const vector<T>& vec);

template<typename T> ostream& operator <<(ostream& os, const vector<vector<T>>& vv);

template<typename T> vector<T> make_v(size_t a);

template<typename T,typename... Ts> auto make_v(size_t a,Ts... ts);

template<typename T,typename V> typename enable_if<is_class<T>::value==0>::type fill_v(T &t,const V &v);

template<typename T,typename V> typename enable_if<is_class<T>::value!=0>::type fill_v(T &t,const V &v);



// implementation

template<typename T>

istream& operator >>(istream& is, vector<T>& vec) {

	for(T& x: vec) is >> x;

	return is;

}

template<typename T1, typename T2>

ostream& operator <<(ostream& os, const pair<T1, T2>& p) {

	os << p.first << "," << p.second;

	return os;

}

template<typename T>

ostream& operator <<(ostream& os, const vector<T>& vec) {

	for(int i=0; i<vec.size(); i++){

		os << vec[i] << ( i+1 == vec.size() ? "" : "\t" );

	}

	return os;

}

template<typename T>

ostream& operator <<(ostream& s, const vector<vector<T>>& vv) {

	for (int i = 0; i < vv.size(); ++i) {

		s << vv[i] << endl;

	}

	return s;

}



// 多重vector

// auto dp=make_v<int>(4,h,w) みたいに使える

template<typename T>

vector<T> make_v(size_t a){return vector<T>(a);}



template<typename T,typename... Ts>

auto make_v(size_t a,Ts... ts){

	return vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...));

}



// 多重vectorのためのfill

// fill_v(dp,0) みたいに使える

template<typename T,typename V>

typename enable_if<is_class<T>::value==0>::type

fill_v(T &t,const V &v){t=v;}



template<typename T,typename V>

typename enable_if<is_class<T>::value!=0>::type

fill_v(T &t,const V &v){

	for(auto &e:t) fill_v(e,v);

}



template<class T,class U> void chmax(T&a,U b){if(a<b)a=b;}

template<class T,class U> void chmin(T&a,U b){if(b<a)a=b;}

template<typename T> T gcd(T a, T b) { return b?gcd(b,a%b):a;}

template<typename T> T lcm(T a, T b) { return a/gcd(a,b)*b;}



//main code



int main(int argc, char *argv[])

{

	LL h,n;

	cin >> h >> n;

	VL a(n), b(n);

	for (int i = 0; i < n; i++) {

		cin >> a[i] >> b[i];

	}

	VL dp(h+1,INT32_MAX);

	dp[0] = 0;

	for (int i = 0; i < h; i++) {

		for (int j = 0; j < n; j++) {

			int k = min(h, i+a[j]);

			dp[k] = min(dp[k], dp[i] + b[j]);

		}

	}

	cout << dp[h] << endl;

	return 0;

}