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| #include<iostream>
#include<queue>
#include<algorithm>
#include<set>
#include<cmath>
#include<vector>
#include<map>
#include<stack>
#include<bitset>
#include<cstdio>
#include<cstring>
#define Swap(a,b) a^=b^=a^=b
#define cini(n) scanf("%d",&n)
#define cinl(n) scanf("%lld",&n)
#define cinc(n) scanf("%c",&n)
#define cins(s) scanf("%s",s)
#define coui(n) printf("%d",n)
#define couc(n) printf("%c",n)
#define coul(n) printf("%lld",n)
#define speed ios_base::sync_with_stdio(0)
#define Max(a,b) a>b?a:b
#define Min(a,b) a<b?a:b
#define mem(n,x) memset(n,x,sizeof(n))
#define INF 0x3f3f3f3f
#define maxn 100010
#define Ege 100000000
#define Vertex 1005
#define esp 1e-9
#define mp(a,b) make_pair(a,b)
using namespace std;
typedef long long ll;
typedef pair<int,int> PII;
struct Node
{
int to, lat, val;
};
Node edge[1000005];
int head[1005],tot,dis[1005],N,M,vis[1005];
void add(int from, int to, int dis)
{
edge[++tot].lat = head[from];
edge[tot].to = to;
edge[tot].val = dis;
head[from] = tot;
}
void spfa(int s)
{
for(int i=0;i<=N;i++) dis[i]=-INF;
dis[0]=0;
memset(vis, 0, sizeof(vis));
vis[s] = 1;
dis[s] = 0;
queue<int>Q;
Q.push(s);
while (!Q.empty())
{
int u = Q.front();
Q.pop();
vis[u] = 0;
for (int i = head[u]; i; i = edge[i].lat)
{
int to = edge[i].to;
int di = edge[i].val;
if (dis[to]<dis[u] + di)
{
dis[to] = dis[u] + di;
if (!vis[to])
{
vis[to] = 1;
Q.push(to);
}
}
}
}
}
int main()
{
int t, x;
memset(head, 0, sizeof(head));
cini(N),cini(M);
while (M--)
{
int a, b, dis;
scanf("%d %d %d", &a, &b, &dis);
add(a, b, dis);
}
spfa(1);
if(dis[N]==-INF) {return cout<<-1<<endl,0;}
cout<<dis[N]<<endl;
return 0;
}
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