# Original solution
#!/usr/bin/env python3
import sys


def solve(H: int, N: int, A: "List[int]", B: "List[int]"):
    hmax = H + max(A)
    cost = [0] * hmax
    intmax = 99999
    magics = [(a, b) for a, b in zip(A,B)]
    for i in range(1, hmax):
        for a, b in magics:
            if i >= a:
                cost[i] = min(cost[i-a]+b, cost[i]) if cost[i] > 0 else cost[i-a]+b
            else:
                cost[i] = min(b, cost[i]) if cost[i] > 0 else b
    #print(cost)
    print((min(cost[H:])))

def solve_dijkstra(H: int, N: int, A: "List[int]", B: "List[int]"):
    nodes = {0: 0}
    fixed = 0
    unfixed = set()
    while True:
        cost = nodes[fixed]
        for a, b in zip(A,B):
            new_node = fixed + a
            last = nodes.get(new_node, 999999999)
            new_cost = cost + b
            if last > new_cost:
                nodes[new_node] = new_cost
                unfixed.add(new_node)
        fixed = min(unfixed)
        if fixed >= H:
            break
        unfixed.remove(fixed)
    print((min([v for k, v in list(nodes.items()) if k >= H])))

# Generated by 1.1.6 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    H = int(next(tokens))  # type: int
    N = int(next(tokens))  # type: int
    A = [int()] * (N)  # type: "List[int]"
    B = [int()] * (N)  # type: "List[int]"
    for i in range(N):
        A[i] = int(next(tokens))
        B[i] = int(next(tokens))
    solve(H, N, A, B)

if __name__ == '__main__':
    main()


# Optimized solution
#!/usr/bin/env python3
import sys


def solve(H: int, N: int, A: "List[int]", B: "List[int]"):
    hmax = H + max(A)
    cost = [0] * hmax
    magics = [(a, b) for a, b in zip(A,B)]
    for i in range(1, hmax):
        for a, b in magics:
            if i >= a:
                cost[i] = min(cost[i-a]+b, cost[i]) if cost[i] > 0 else cost[i-a]+b
            else:
                cost[i] = min(b, cost[i]) if cost[i] > 0 else b
    #print(cost)
    print((min(cost[H:])))

def solve_dijkstra(H: int, N: int, A: "List[int]", B: "List[int]"):
    nodes = {0: 0}
    fixed = 0
    unfixed = set()
    while True:
        cost = nodes[fixed]
        for a, b in zip(A,B):
            new_node = fixed + a
            last = nodes.get(new_node, 999999999)
            new_cost = cost + b
            if last > new_cost:
                nodes[new_node] = new_cost
                unfixed.add(new_node)
        fixed = min(unfixed)
        if fixed >= H:
            break
        unfixed.remove(fixed)
    print((min([v for k, v in list(nodes.items()) if k >= H])))

# Generated by 1.1.6 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    H = int(next(tokens))  # type: int
    N = int(next(tokens))  # type: int
    A = [int()] * (N)  # type: "List[int]"
    B = [int()] * (N)  # type: "List[int]"
    for i in range(N):
        A[i] = int(next(tokens))
        B[i] = int(next(tokens))
    solve(H, N, A, B)

if __name__ == '__main__':
    main()