C, N = map(int, input().split())
info = []
for _ in range(N) :
    info.append(tuple(map(int, input().split())))

INF = float("inf")
dp = [INF if i != 0 else 0 for i in range(C+101)]

for cost, man in info :
    for i in range(man, C+101) :
        if dp[i-man] != INF :
            dp[i] = min(dp[i], dp[i-man] + cost)

print(min(dp[C:]))