Number of vertices DFS

n, s = map(int, input().split())

adj = []
while n:
    adj.append(list(map(int, input().split())))
    n -= 1

s -= 1 # convert to zero-based
st = [s]
res = 0
visited = [0] * len(adj)
visited[s] = 1

while st:
    cur = st.pop()
    res += 1

    for v, edge in enumerate(adj[cur]):
        if edge and not visited[v]:
            st.append(v)
            visited[v] = 1

print(res)