# Arup Guha
# 11/8/2025
# SER D2 Problem F: Breakout

toks = input().split()
n = int(toks[0])
leave = int(toks[1])
crates = int(toks[2])

freq = []
for i in range(n+1):
    freq.append(0)

# Frequency of crates.
for i in range(crates):
    freq[int(input())] += 1

# Go forwards.
forward = 0
for i in range(1,leave):
    forward += freq[i]

# Go backwards.
back = 0
for i in range(n,leave-1,-1):
    back += freq[i]

# Take better one.
print(min(forward, back))