t,m =map(int,input().split(" "))
tm = []
vl = []
for i in range(m):
    a,b = map(int,input().split(" "))
    tm.append(a)
    vl.append(b)

#该初始化代表背包不一定要装满
dp = [0 for j in range(t+1)]
#t是时间，m是草药数目
for i in range(1, m+1):
    #注意：第二层循环要逆序循环
    for j in range(t, 0, -1):#可优化成 for j in range(v, cost[i]-1, -1):
        if j >= vl[i-1]:
            dp[j] = max(dp[j], dp[j-vl[i-1]]+vl[i-1])

print(int(dp[m]))