// Slower C++ solution:
#include <bits/stdc++.h>

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

#define mrep(i,j,n) for(int i = j; i < n; i++)

#define reps(i,n) for(int i = 1; i <= n; i++)

#define rrep(i,n) for(int i = n-1; i >= 0; i--)

#define mreps(i,j,n) for(int i = j; i <= n; i++)

#define rreps(i,n) for(int i = n; i >= 1; i--)

#define co(x) cout << x <<endl

#define cs(x) cout << x <<" "

#define el cout << endl

#define sp(x) cout << setprecision(x);

#define cer(x) cerr << x <<endl

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

#define sz(x) ((int)(x).size())

#define ERASE(x,val) x.erase(remove(ALL(x), val), x.end())

#define vi vector<int> 

#define vvi vector<vector<int>> 

#define vpii vector<pair<int,int>> 

#define vl vector<ll> 

#define vvl vector<vector<ll>> 

#define vd vector<double> 

#define vvd vector<vector<double>> 

#define vb vector<bool> 

#define vvb vector<vector<bool>>

#define vs vector<string>

typedef long long ll;

typedef unsigned long long ull;

using namespace std;

ll mod = 1e9 + 7;

ll inf = 1001001000;

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

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

ll gcd(ll a, ll b) { return b ? gcd(b, a % b) : a; }

ll lcm(ll a, ll b) { ll g = gcd(a, b); return a * b / g; }

bool is_prime(ll x) { for (ll i = 2; i * i <= x; i++) { if (x % i == 0)return false; } return true; }





int main()

{

	cin.tie(0);

	ios::sync_with_stdio(false);

	ll h, n; cin >> h >> n;

	vl a(n), b(n);

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

	vvl dp(n + 1, vl(h+1, inf));

	dp[0][0] = 0;

	rep(i, n)rep(j, h + 1)

	{

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

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

	}

	ll ans = dp[n][h];

	co(ans);

	return 0;

}


// Faster C++ solution for the same problem (measured speedup: 2.160041160649105x):
#include <bits/stdc++.h>

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

#define mrep(i,j,n) for(int i = j; i < n; i++)

#define reps(i,n) for(int i = 1; i <= n; i++)

#define rrep(i,n) for(int i = n-1; i >= 0; i--)

#define mreps(i,j,n) for(int i = j; i <= n; i++)

#define rreps(i,n) for(int i = n; i >= 1; i--)

#define co(x) cout << x <<endl

#define cs(x) cout << x <<" "

#define el cout << endl

#define sp(x) cout << setprecision(x);

#define cer(x) cerr << x <<endl

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

#define sz(x) ((int)(x).size())

#define ERASE(x,val) x.erase(remove(ALL(x), val), x.end())

#define vi vector<int> 

#define vvi vector<vector<int>> 

#define vpii vector<pair<int,int>> 

#define vl vector<ll> 

#define vvl vector<vector<ll>> 

#define vd vector<double> 

#define vvd vector<vector<double>> 

#define vb vector<bool> 

#define vvb vector<vector<bool>>

#define vs vector<string>

typedef long long ll;

typedef unsigned long long ull;

using namespace std;

ll mod = 1e9 + 7;

ll inf = 1001001000;

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

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

ll gcd(ll a, ll b) { return b ? gcd(b, a % b) : a; }

ll lcm(ll a, ll b) { ll g = gcd(a, b); return a * b / g; }

bool is_prime(ll x) { for (ll i = 2; i * i <= x; i++) { if (x % i == 0)return false; } return true; }





int main()

{

	cin.tie(0);

	ios::sync_with_stdio(false);

	ll h, n; cin >> h >> n;

	vl a(n), b(n);

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

	vl dp(h+1, inf);

	dp[0] = 0;

	rep(i, n)rep(j, h + 1)

	{

		chmin(dp[min(h, j + a[i])], dp[j] + b[i]);

	}

	ll ans = dp[h];

	co(ans);

	return 0;

}