# coding: utf-8

def walk(cur, lines):
    mid = lines[cur[0]]
    left = lines[cur[0] - 1]
    height = cur[1]
    lowest = 0
    next_line = []
    for i, j in mid:
        if i > lowest and i < height:
            lowest = i
            next_line = [cur[0] + 1, j]
    for j, i in left:
        if i > lowest and i < height:
            lowest = i
            next_line = [cur[0] - 1, j]
    if len(next_line) == 0:
        return cur[0]
    else:
        return walk(next_line, lines)

L, n, m = map(int, raw_input().strip().split())
lines = [[] for i in range(n + 1)]
for i in range(m):
    x, l, r =  map(int, raw_input().strip().split())
    lines[x].append([l, r])
line = walk([1, L], lines)
print line