2828.py

# 사과 담기 게임
import sys

sys.stdin.readline

N, M = map(int, input().split())
J = int(input())
l = 1
r = M

cnt = 0
for _ in range(J):
    i = int(input())
    if l <= i <= r:
        continue
    if i < l:
        cnt += l - i
        l = i
        r = l + M - 1
    else:
        cnt += i - r
        r = i
        l = r - M + 1

print(cnt)