n,m,s,t=list(map(int,input().split()))
w=[[float('inf') for i in range(n+1)] for j in range(n+1)]
for i in range(m):
    u,v,ww=list(map(int,input().split()))
    w[u][v],w[v][u]=ww,ww
v=[float('inf') for i in range(n+1)]
vis=[0 for i in range(n+1)]
v[s]=0
vis[s]=1
k=s
while vis[t]==0:
    min=float('inf')
    for i in range(1,n+1):
        if i==k or vis[i]!=0:
            continue
        if v[k]+w[k][i]<v[i]:
            v[i]=v[k]+w[k][i]
    for i in range(1,n+1):
        if vis[i]==0 and v[i]<min:
            min=v[i]
            k=i
    vis[k]=1
print(v[t])

蒟蒻不学无术，不知道怎么解决