import sys

def main():
    input = sys.stdin.read().split()
    idx = 0
    N = int(input[idx])
    idx += 1
    points = []
    for _ in range(N):
        x = int(input[idx])
        y = int(input[idx+1])
        points.append((x, y))
        idx += 2
    
    if N == 1:
        print(0)
        return
    
    x0, y0 = points[0]
    d1_sq = []
    for i in range(1, N):
        xi, yi = points[i]
        dx = xi - x0
        dy = yi - y0
        d1_sq.append(dx*dx + dy*dy)
    
    has_edge = [False] * (N-1)
    
    for i in range(N-1):
        xi, yi = points[i+1]
        for j in range(i+1, N-1):
            xj, yj = points[j+1]
            dx = xi - xj
            dy = yi - yj
            dij_sq = dx*dx + dy*dy
            if dij_sq < d1_sq[i] and dij_sq < d1_sq[j]:
                has_edge[i] = True
                has_edge[j] = True
    
    count = sum(has_edge)
    print((N-1) - count)

if __name__ == "__main__":
    main()