import sys

def main():
    N, M = map(int, sys.stdin.readline().split())
    out_degree = [0] * (N + 1)
    in_degree = [0] * (N + 1)
    for _ in range(M):
        u, v = map(int, sys.stdin.readline().split())
        out_degree[u] += 1
        in_degree[v] += 1
    sum_pos = 0
    for u in range(1, N+1):
        delta = out_degree[u] - in_degree[u]
        if delta > 0:
            sum_pos += delta
    if sum_pos == 0:
        print(0)
    else:
        print(sum_pos - 1)

if __name__ == "__main__":
    main()