n,m=map(int,input().split())
C=[0]+[0]*n
for i in range(m):
    a,b,c=map(int,input().split())
    C[a]+=c
    C[b]+=c

C.sort(reverse=True)
for i in range(1,n,2):
    C[i]*=-1
ans=sum(C)//2
print(ans)