t, n = map(int, input().split())
value = [0]
ti = [0]
for i in range(n):
    a, b = map(int, input().split())
    value.append(b)
    ti.append(a)
dp = [[0 for i in range(t+1)]]
for i in range(1, n+1):
    lst = [0]
    for k in range(1, t+1):
        if ti[i] <= k:
            lst.append(max(dp[-1][k], value[i]+lst[k-ti[i]]))
        else:
            lst.append(dp[-1][k])
    dp.append(lst)
print(dp[-1][-1])