### BUGGY CODE ###

#import sys
MOD = 10 ** 9 + 7
INFI = 10**10
#input = sys.stdin.readline
import math

import itertools

#import bisect

import copy
from functools import lru_cache

def sosuhante(n):
    for k in range(2, int(math.sqrt(n))+1):
        if n% k ==0:
            return False
    return True
def cmb(n, r):
    if n - r < r: r = n - r
    if r == 0: return 1
    if r == 1: return n

    numerator = [n - r + k + 1 for k in range(r)]
    denominator = [k + 1 for k in range(r)]

    for p in range(2,r+1):
        pivot = denominator[p - 1]
        if pivot > 1:
            offset = (n - r) % p
            for k in range(p-1,r,p):
                numerator[k - offset] /= pivot
                denominator[k] /= pivot

    result = 1
    for k in range(r):
        if numerator[k] > 1:
            result *= int(numerator[k])

    return result

def kingaku(a,b,n):
    keta=len(str(n))
    return a*n+b*keta

def my_index(l, x, default=False):
    if x in l:
        return l.index(x)
    else:
        return default

#    h,w,a,b = map(int, input().split())
#    c = [[0 for j in range(n)] for i in range(n)]



def main():
    h,n=map(int,input().split()) #n yen, m types
    a=[]
    b=[]
    for i in range(n):
        x,y=map(int,input().split())
        a.append(x)
        b.append(y)

    dp=[INFI for i in range(h+1)]
    dp[0]=0

    @lru_cache(maxsize=None)
    def f(h):

        for i in range(n):
            for j in range(h+1):
                if j-a[i]<0:
                    dp[j] = min(dp[j], dp[0] + b[i])
                else:
                    dp[j]=min(dp[j],dp[j-a[i]]+b[i])
        return dp[h]

    print(f(h))


if __name__ == "__main__":
    main()

### FIXED CODE ###

#import sys
MOD = 10 ** 9 + 7
INFI = 10**10
#input = sys.stdin.readline
import math
 
import itertools
 
#import bisect
 
import copy
 
 
def sosuhante(n):
    for k in range(2, int(math.sqrt(n))+1):
        if n% k ==0:
            return False
    return True
def cmb(n, r):
    if n - r < r: r = n - r
    if r == 0: return 1
    if r == 1: return n
 
    numerator = [n - r + k + 1 for k in range(r)]
    denominator = [k + 1 for k in range(r)]
 
    for p in range(2,r+1):
        pivot = denominator[p - 1]
        if pivot > 1:
            offset = (n - r) % p
            for k in range(p-1,r,p):
                numerator[k - offset] /= pivot
                denominator[k] /= pivot
 
    result = 1
    for k in range(r):
        if numerator[k] > 1:
            result *= int(numerator[k])
 
    return result
 
def kingaku(a,b,n):
    keta=len(str(n))
    return a*n+b*keta
 
def my_index(l, x, default=False):
    if x in l:
        return l.index(x)
    else:
        return default
 
#    h,w,a,b = map(int, input().split())
#    c = [[0 for j in range(n)] for i in range(n)]
 
 
 
def main():
    h,n=map(int,input().split()) #n yen, m types
    a=[]
    b=[]
    for i in range(n):
        x,y=map(int,input().split())
        a.append(x)
        b.append(y)
 
    dp=[INFI for i in range(h+1)]
    dp[0]=0
    for i in range(n):
        for j in range(len(dp)):
            if j-a[i]<0:
                dp[j] = min(dp[j], dp[0] + b[i])
            else:
                dp[j]=min(dp[j],dp[j-a[i]]+b[i])
 
    print(dp[h])
 
 
if __name__ == "__main__":
    main()