#include <iostream>
#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <cstring>
#include <deque>
#include <functional>
#include <initializer_list>
#include <math.h>
#include <map>
#include <random>
#include <set>
#include <stack>
#include <tuple>
#include <type_traits>
#include <queue>
#include <vector>


#define FOR(i, a, b) for(int (i) = (a); (i) < (b); ++(i))
#define rFOR(i, a, b) for(int (i) = (b); (i) >= (a); --(i))
#define REP(i, n) FOR(i, 0, n)
#define rREP(i, n) rFOR(i, 0, (n-1))
#define SORT(A) std::sort((A).begin(), (A).end())
#define ALL(A) (A).begin(), (A).end()
// 座標圧縮 (for vector) : ソートしてから使うのが一般的 ; SORT(A) => COORDINATE_COMPRESSION(A)
#define COORDINATE_COMPRESSION(A) (A).erase(unique((A).begin(),(A).end()),(A).end())

using lli = long long int;
using pii = std::pair<int, int>;

// グリッド上の縦横移動
constexpr std::array<std::pair<int, int>, 4> dxdy = {
    std::pair<int, int>( 1,  0),
    std::pair<int, int>(-1,  0),
    std::pair<int, int>( 0,  1),
    std::pair<int, int>( 0, -1)
};

void VintOut(std::vector<int>& A){
    const int n = A.size();
    if(n == 0){putchar('\n'); return;}
    printf("%d", A[0]);
    for(int i = 1; i < n; ++i) printf(" %d", A[i]);
    putchar('\n');
}
void VintOut(std::vector<long long int>& A){
    const int n = A.size();
    if(n == 0){ putchar('\n'); return;}
    printf("%lld", A[0]);
    for(int i = 1; i < n; ++i) printf(" %lld", A[i]);
    putchar('\n');
}

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

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

inline bool isIn(int x, int y, int H, int W){
    return 0 <= x and x < H and 0 <= y and y < W;
}
inline bool bitUP(int state, int k){ return (state >> k) & 1; }
inline bool bitUP(long long int state, int k){ return (state >> k) & 1;}

// z-algorithm
template <class T> std::vector<int> z_algorithm(const T &str) {
    const int n = str.size();
    std::vector<int> resOfCP(n); resOfCP[0] = n;
    int i = 1, j = 0;
    while (i < n) {
        while (i + j < n and str[j] == str[i + j]) ++j;
        resOfCP[i] = j;
        if (j == 0) { ++i; continue;}
        int k = 1;
        while (i + k < n and k + resOfCP[k] < j) resOfCP[i + k] = resOfCP[k], ++k;
        i += k; j -= k;
    }
    return resOfCP;
}


// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

constexpr lli inf = 1e18 + 114514;
constexpr int MAX_N = 1e3;
constexpr int MAX_H = 1e4;
std::array<std::array<lli, MAX_H + 1>, MAX_N + 1> DP;

int main(void){
    int H, n; scanf("%d%d", &H, &n);
    for(int i = 0; i <= n; ++i) for(int j = 0; j <= H; ++j) DP[i][j] = inf;
    DP[0][H] = 0;
    REP(i, n){
        int a, b; scanf("%d%d", &a, &b);
        for(int j = 0; j <= H; ++j){
            int nj = j - a; if(nj < 0) nj = 0;
            chmin(DP[i+1][nj], DP[i][j] + b);
            chmin(DP[i+1][j],  DP[i][j]);
        }
        for(int j = H; j >= 0; --j){
            int nj = j - a; if(nj < 0) nj = 0;
            chmin(DP[i+1][nj], DP[i+1][j] + b);
        }
    }
    printf("%lld\n", DP[n][0]);
    
    
    return 0;
}

Measured memory_bytes: 78464