import sys

sys.setrecursionlimit(10**6)
int1 = lambda x: int(x)-1
p2D = lambda x: print(*x, sep="\n")
def II(): return int(sys.stdin.buffer.readline())
def MI(): return map(int, sys.stdin.buffer.readline().split())
def MI1(): return map(int1, sys.stdin.buffer.readline().split())
def LI(): return list(map(int, sys.stdin.buffer.readline().split()))
def LI1(): return list(map(int1, sys.stdin.buffer.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def BI(): return sys.stdin.buffer.readline().rstrip()
def SI(): return sys.stdin.buffer.readline().rstrip().decode()
dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
inf = 10**16
# md = 998244353
md = 10**9+7

t = II()
n, m = MI()
to = [[] for _ in range(n)]
for _ in range(m):
    u, v, w = MI()
    u, v = u-1, v-1
    to[u].append((v, w))
    if t == 0:
        to[v].append((u, w))

vis = [-1]*n
dist = [-1]*n
def dfs(u):
    dist[u] = 0
    stack = [(u,-1,0)]
    res = inf
    while stack:
        u,pu,d = stack.pop()
        # print(u,pu,d,dist,stack)
        dist[u]=d
        if vis[u] == 0:
            vis[u] = -1
        else:
            vis[u] = 0
            stack.append((u,pu,d))
            for v, w in to[u]:
                if v==pu:continue
                if vis[v] == 0:
                    # print(u,v,d+w-dist[v])
                    res = min(res, d+w-dist[v])
                elif vis[v] == -1:
                    stack.append((v,u,d+w))
    return res

ans=inf
for u in range(n):
    if vis[u]==1:continue
    ans=min(ans,dfs(u))

if ans==inf:print(-1)
else:print(ans)