import math
import statistics


T = []

W = []

T.append(0)
W.append(0)

def  dp(m,t):
    if m==0 or t==0:
        temp = 0
    elif t<T[m]:
        return dp(m-1,t)
    else:
        temp1 = dp(m-1,t)
        temp2 = W[m]+dp(m-1,t-T[m])
        temp = max(temp1,temp2)

    return temp
t,m = list(map(int,input().split()))

for i in range(m):
    x = list(map(int,input().split()))

    T.append(x[0])
    W.append(x[1])

print(dp(m,t))