Buggy python submission (verdict: Time Limit Exceeded):
N,M = map(int,input().split())
LRC = [list(map(int,input().split())) for _ in range(M)]

def dijkstra(s,n,cost):
  #始点sから各頂点への最短距離
  #n:頂点数,　cost[u][v] : 辺uvのコスト(存在しないときはinf)
  d = [float("inf")] * n
  used = [False] * n
  d[s] = 0

  while True:
    v = -1
    #まだ使われてない頂点の中から最小の距離のものを探す
    for i in range(n):
      if (not used[i]) and (v == -1):
        v = i
      elif (not used[i]) and d[i] < d[v]:
        v = i
    if v == -1:
      break
    used[v] = True

    for j in range(n):
      d[j] = min(d[j],d[v]+cost[v][j])
  return d

INF = float('inf')
G = [[INF for _ in range(N)] for _ in range(N)]

for i in range(N-1):
  G[i+1][i] = 0
for l,r,c in LRC:
  l -= 1
  r -= 1
  G[l][r] = c
#print(G)

#print(dijkstra(0,N,G))
p = dijkstra(0,N,G)[N-1]
print(p if p != INF else -1)

Fixed submission:
class SegmentTree:
  def __init__(self, size, default, op = min):
    self.size = 2**size.bit_length()
    self.dat = [default]*(self.size*2)
    self.op = op

  def update(self, i, x):
    i += self.size
    self.dat[i] = x
    while i > 0:
      i >>= 1
      self.dat[i] = self.op(self.dat[i*2], self.dat[i*2+1])

  def add(self, i, x):
    i += self.size
    self.dat[i] = self.op(self.dat[i], x)
    while i > 0:
      i >>= 1
      self.dat[i] = self.op(self.dat[i], x)

  def get(self, a, b = None):
    if b is None:
      b = a + 1
    l, r = a + self.size, b + self.size
    res = None
    while l < r:
      if l & 1:
        if res is None:
          res = self.dat[l]
        else:
          res = self.op(res, self.dat[l])
        l += 1

      if r & 1:
        r -= 1
        if res is None:
          res = self.dat[r]
        else:
          res = self.op(res, self.dat[r])
      l >>= 1
      r >>= 1
    return res

N,M = map(int,input().split())
LRC = [list(map(int,input().split())) for _ in range(M)]
LRC.sort(key=lambda x:(x[0],x[1]))
#print(LRC)

INF = 10**18
dp = SegmentTree(N,INF,min)
dp.update(0,0)
#print(dp.get(0,1))

for l,r,c in LRC:
  p = dp.get(l-1,r-1)+c
  # cf.https://ikatakos.com/pot/programming_algorithm/contest_history/atcoder/2019/1109_nikkei2019-2-qual
  #for i in range(l,r):
  #  if p < dp.get(i):
  #    dp.update(i,p)
  if p < dp.get(r-1):
    dp.update(r-1,p)
print(dp.get(N-1) if dp.get(N-1) != INF else -1)

Buggy python submission (verdict: Time Limit Exceeded):
class SegmentTree:
  def __init__(self, size, default, op = min):
    self.size = 2**size.bit_length()
    self.dat = [default]*(self.size*2)
    self.op = op

  def update(self, i, x):
    i += self.size
    self.dat[i] = x
    while i > 0:
      i >>= 1
      self.dat[i] = self.op(self.dat[i*2], self.dat[i*2+1])

  def add(self, i, x):
    i += self.size
    self.dat[i] = self.op(self.dat[i], x)
    while i > 0:
      i >>= 1
      self.dat[i] = self.op(self.dat[i], x)

  def get(self, a, b = None):
    if b is None:
      b = a + 1
    l, r = a + self.size, b + self.size
    res = None
    while l < r:
      if l & 1:
        if res is None:
          res = self.dat[l]
        else:
          res = self.op(res, self.dat[l])
        l += 1

      if r & 1:
        r -= 1
        if res is None:
          res = self.dat[r]
        else:
          res = self.op(res, self.dat[r])
      l >>= 1
      r >>= 1
    return res

N,M = map(int,input().split())
LRC = [list(map(int,input().split())) for _ in range(M)]
LRC.sort(key=lambda x:(x[0],x[1]))
#print(LRC)

INF = 10**18
dp = SegmentTree(N,INF,min)
dp.update(0,0)
#print(dp.get(0,1))

for l,r,c in LRC:
  p = dp.get(l-1,r-1)+c
  for i in range(l,r):
    if p < dp.get(i):
      dp.update(i,p)
print(dp.get(N-1) if dp.get(N-1) != INF else -1)


Fixed submission:
class SegmentTree:
  def __init__(self, size, default, op = min):
    self.size = 2**size.bit_length()
    self.dat = [default]*(self.size*2)
    self.op = op

  def update(self, i, x):
    i += self.size
    self.dat[i] = x
    while i > 0:
      i >>= 1
      self.dat[i] = self.op(self.dat[i*2], self.dat[i*2+1])

  def add(self, i, x):
    i += self.size
    self.dat[i] = self.op(self.dat[i], x)
    while i > 0:
      i >>= 1
      self.dat[i] = self.op(self.dat[i], x)

  def get(self, a, b = None):
    if b is None:
      b = a + 1
    l, r = a + self.size, b + self.size
    res = None
    while l < r:
      if l & 1:
        if res is None:
          res = self.dat[l]
        else:
          res = self.op(res, self.dat[l])
        l += 1

      if r & 1:
        r -= 1
        if res is None:
          res = self.dat[r]
        else:
          res = self.op(res, self.dat[r])
      l >>= 1
      r >>= 1
    return res

N,M = map(int,input().split())
LRC = [list(map(int,input().split())) for _ in range(M)]
LRC.sort(key=lambda x:(x[0],x[1]))
#print(LRC)

INF = 10**18
dp = SegmentTree(N,INF,min)
dp.update(0,0)
#print(dp.get(0,1))

for l,r,c in LRC:
  p = dp.get(l-1,r-1)+c
  # cf.https://ikatakos.com/pot/programming_algorithm/contest_history/atcoder/2019/1109_nikkei2019-2-qual
  #for i in range(l,r):
  #  if p < dp.get(i):
  #    dp.update(i,p)
  if p < dp.get(r-1):
    dp.update(r-1,p)
print(dp.get(N-1) if dp.get(N-1) != INF else -1)

Buggy python submission (verdict: Time Limit Exceeded):
class SegmentTree:
  def __init__(self, size, default, op = min):
    self.size = 2**size.bit_length()
    self.dat = [default]*(self.size*2)
    self.op = op

  def update(self, i, x):
    i += self.size
    self.dat[i] = x
    while i > 0:
      i >>= 1
      self.dat[i] = self.op(self.dat[i*2], self.dat[i*2+1])

  def add(self, i, x):
    i += self.size
    self.dat[i] = self.op(self.dat[i], x)
    while i > 0:
      i >>= 1
      self.dat[i] = self.op(self.dat[i], x)

  def get(self, a, b = None):
    if b is None:
      b = a + 1
    l, r = a + self.size, b + self.size
    res = None
    while l < r:
      if l & 1:
        if res is None:
          res = self.dat[l]
        else:
          res = self.op(res, self.dat[l])
        l += 1

      if r & 1:
        r -= 1
        if res is None:
          res = self.dat[r]
        else:
          res = self.op(res, self.dat[r])
      l >>= 1
      r >>= 1
    return res

N,M = map(int,input().split())
LRC = [list(map(int,input().split())) for _ in range(M)]
LRC.sort(key=lambda x:(x[0],x[1]))
#print(LRC)

INF = 10**18
dp = SegmentTree(N,INF,min)
dp.update(0,0)
#print(dp.get(0,1))

for l,r,c in LRC:
  p = dp.get(l-1,r-1)+c
  for i in range(l,r):
    dp.update(i,min(p,dp.get(i)))
print(dp.get(N-1) if dp.get(N-1) != INF else -1)


Fixed submission:
class SegmentTree:
  def __init__(self, size, default, op = min):
    self.size = 2**size.bit_length()
    self.dat = [default]*(self.size*2)
    self.op = op

  def update(self, i, x):
    i += self.size
    self.dat[i] = x
    while i > 0:
      i >>= 1
      self.dat[i] = self.op(self.dat[i*2], self.dat[i*2+1])

  def add(self, i, x):
    i += self.size
    self.dat[i] = self.op(self.dat[i], x)
    while i > 0:
      i >>= 1
      self.dat[i] = self.op(self.dat[i], x)

  def get(self, a, b = None):
    if b is None:
      b = a + 1
    l, r = a + self.size, b + self.size
    res = None
    while l < r:
      if l & 1:
        if res is None:
          res = self.dat[l]
        else:
          res = self.op(res, self.dat[l])
        l += 1

      if r & 1:
        r -= 1
        if res is None:
          res = self.dat[r]
        else:
          res = self.op(res, self.dat[r])
      l >>= 1
      r >>= 1
    return res

N,M = map(int,input().split())
LRC = [list(map(int,input().split())) for _ in range(M)]
LRC.sort(key=lambda x:(x[0],x[1]))
#print(LRC)

INF = 10**18
dp = SegmentTree(N,INF,min)
dp.update(0,0)
#print(dp.get(0,1))

for l,r,c in LRC:
  p = dp.get(l-1,r-1)+c
  # cf.https://ikatakos.com/pot/programming_algorithm/contest_history/atcoder/2019/1109_nikkei2019-2-qual
  #for i in range(l,r):
  #  if p < dp.get(i):
  #    dp.update(i,p)
  if p < dp.get(r-1):
    dp.update(r-1,p)
print(dp.get(N-1) if dp.get(N-1) != INF else -1)

Buggy python submission (verdict: Time Limit Exceeded):
class SegmentTree:
  def __init__(self, size, default, op = min):
    self.size = 2**size.bit_length()
    self.dat = [default]*(self.size*2)
    self.op = op

  def update(self, i, x):
    i += self.size
    self.dat[i] = x
    while i > 0:
      i >>= 1
      self.dat[i] = self.op(self.dat[i*2], self.dat[i*2+1])

  def add(self, i, x):
    i += self.size
    self.dat[i] = self.op(self.dat[i], x)
    while i > 0:
      i >>= 1
      self.dat[i] = self.op(self.dat[i], x)

  def get(self, a, b = None):
    if b is None:
      b = a + 1
    l, r = a + self.size, b + self.size
    res = None
    while l < r:
      if l & 1:
        if res is None:
          res = self.dat[l]
        else:
          res = self.op(res, self.dat[l])
        l += 1

      if r & 1:
        r -= 1
        if res is None:
          res = self.dat[r]
        else:
          res = self.op(res, self.dat[r])
      l >>= 1
      r >>= 1
    return res

N,M = map(int,input().split())
LRC = [list(map(int,input().split())) for _ in range(M)]
LRC.sort(key=lambda x:(x[0],x[1]))
#print(LRC)

INF = 10**18
dp = SegmentTree(N,INF,min)
dp.update(0,0)
#print(dp.get(0,1))

for l,r,c in LRC:
  for i in range(l,r):
    p = dp.get(l-1,r-1)+c
    dp.update(i,min(p,dp.get(i)))
print(dp.get(N-1) if dp.get(N-1) != INF else -1)


Fixed submission:
class SegmentTree:
  def __init__(self, size, default, op = min):
    self.size = 2**size.bit_length()
    self.dat = [default]*(self.size*2)
    self.op = op

  def update(self, i, x):
    i += self.size
    self.dat[i] = x
    while i > 0:
      i >>= 1
      self.dat[i] = self.op(self.dat[i*2], self.dat[i*2+1])

  def add(self, i, x):
    i += self.size
    self.dat[i] = self.op(self.dat[i], x)
    while i > 0:
      i >>= 1
      self.dat[i] = self.op(self.dat[i], x)

  def get(self, a, b = None):
    if b is None:
      b = a + 1
    l, r = a + self.size, b + self.size
    res = None
    while l < r:
      if l & 1:
        if res is None:
          res = self.dat[l]
        else:
          res = self.op(res, self.dat[l])
        l += 1

      if r & 1:
        r -= 1
        if res is None:
          res = self.dat[r]
        else:
          res = self.op(res, self.dat[r])
      l >>= 1
      r >>= 1
    return res

N,M = map(int,input().split())
LRC = [list(map(int,input().split())) for _ in range(M)]
LRC.sort(key=lambda x:(x[0],x[1]))
#print(LRC)

INF = 10**18
dp = SegmentTree(N,INF,min)
dp.update(0,0)
#print(dp.get(0,1))

for l,r,c in LRC:
  p = dp.get(l-1,r-1)+c
  # cf.https://ikatakos.com/pot/programming_algorithm/contest_history/atcoder/2019/1109_nikkei2019-2-qual
  #for i in range(l,r):
  #  if p < dp.get(i):
  #    dp.update(i,p)
  if p < dp.get(r-1):
    dp.update(r-1,p)
print(dp.get(N-1) if dp.get(N-1) != INF else -1)

Buggy python submission (verdict: Time Limit Exceeded):
class SegmentTree:
  def __init__(self, size, default, op = min):
    self.size = 2**size.bit_length()
    self.dat = [default]*(self.size*2)
    self.op = op

  def update(self, i, x):
    i += self.size
    self.dat[i] = x
    while i > 0:
      i >>= 1
      self.dat[i] = self.op(self.dat[i*2], self.dat[i*2+1])

  def add(self, i, x):
    i += self.size
    self.dat[i] = self.op(self.dat[i], x)
    while i > 0:
      i >>= 1
      self.dat[i] = self.op(self.dat[i], x)

  def get(self, a, b = None):
    if b is None:
      b = a + 1
    l, r = a + self.size, b + self.size
    res = None
    while l < r:
      if l & 1:
        if res is None:
          res = self.dat[l]
        else:
          res = self.op(res, self.dat[l])
        l += 1

      if r & 1:
        r -= 1
        if res is None:
          res = self.dat[r]
        else:
          res = self.op(res, self.dat[r])
      l >>= 1
      r >>= 1
    return res

N,M = map(int,input().split())
LRC = [list(map(int,input().split())) for _ in range(M)]
LRC.sort(key=lambda x:(x[0],x[1]))
#print(LRC)

INF = 10**18
dp = SegmentTree(N,INF,min)
dp.update(0,0)
#print(dp.get(0,1))

for l,r,c in LRC:
  for i in range(l,r):
    dp.update(i,min(dp.get(l-1,i)+c,dp.get(i)))
print(dp.get(N-1) if dp.get(N-1) != INF else -1)


Fixed submission:
class SegmentTree:
  def __init__(self, size, default, op = min):
    self.size = 2**size.bit_length()
    self.dat = [default]*(self.size*2)
    self.op = op

  def update(self, i, x):
    i += self.size
    self.dat[i] = x
    while i > 0:
      i >>= 1
      self.dat[i] = self.op(self.dat[i*2], self.dat[i*2+1])

  def add(self, i, x):
    i += self.size
    self.dat[i] = self.op(self.dat[i], x)
    while i > 0:
      i >>= 1
      self.dat[i] = self.op(self.dat[i], x)

  def get(self, a, b = None):
    if b is None:
      b = a + 1
    l, r = a + self.size, b + self.size
    res = None
    while l < r:
      if l & 1:
        if res is None:
          res = self.dat[l]
        else:
          res = self.op(res, self.dat[l])
        l += 1

      if r & 1:
        r -= 1
        if res is None:
          res = self.dat[r]
        else:
          res = self.op(res, self.dat[r])
      l >>= 1
      r >>= 1
    return res

N,M = map(int,input().split())
LRC = [list(map(int,input().split())) for _ in range(M)]
LRC.sort(key=lambda x:(x[0],x[1]))
#print(LRC)

INF = 10**18
dp = SegmentTree(N,INF,min)
dp.update(0,0)
#print(dp.get(0,1))

for l,r,c in LRC:
  p = dp.get(l-1,r-1)+c
  # cf.https://ikatakos.com/pot/programming_algorithm/contest_history/atcoder/2019/1109_nikkei2019-2-qual
  #for i in range(l,r):
  #  if p < dp.get(i):
  #    dp.update(i,p)
  if p < dp.get(r-1):
    dp.update(r-1,p)
print(dp.get(N-1) if dp.get(N-1) != INF else -1)