http://codeforces.com/problemset/problem/376/B
题意:还债,可相互抵消,问全部人需要还的债共多少;
思路:维护每个人的荷包就行,欠钱的就加到ans就行;
#include<algorithm>
#include<set>
#include<vector>
#include<queue>
#include<cmath>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<set>
#include<vector>
#include<queue>
#include<cmath>
#include<cstring>
#include<sstream>
#include<cstdio>
#include<ctime>
#include<map>
#include<stack>
#include<string>
using namespace std;
#define sfi(i) scanf("%d",&i)
#define pri(i) printf("%d\n",i)
#define sff(i) scanf("%lf",&i)
#define ll long long
#define mem(x,y) memset(x,y,sizeof(x))
#define INF 0x3f3f3f3f
#define eps 1e-6
#define PI acos(-1)
#define lowbit(x) ((x)&(-x))
#define zero(x) (((x)>0?(x):-(x))<eps)
#define fl() printf("flag\n")
ll gcd(ll a,ll b){while(b^=a^=b^=a%=b);return a;}
const int maxn=1e6+9;
const int mod=1e9+7;
template <class T>
inline void sc(T &ret)
{
char c;
ret = 0;
while ((c = getchar()) < '0' || c > '9');
while (c >= '0' && c <= '9')
{
ret = ret * 10 + (c - '0'), c = getchar();
}
}
int num[maxn];
int main()
{
int n,m;
cin>>n>>m;
for(int i=0;i<m;i++)
{
int a,b,x;
cin>>a>>b>>x;
num[a]-=x;
num[b]+=x;
}
ll ans=0;
for(int i=1;i<=n;i++)
{
ans+=(num[i]>0?num[i]:0);
}
cout<<ans<<endl;
return 0;
}