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_plus = 0
    for i in range(1, N+1):
        delta = out_degree[i] - in_degree[i]
        if delta > 0:
            sum_plus += delta
    
    K = abs(sum_plus - 1)
    print(K)

if __name__ == "__main__":
    main()