T165T3

#include<bits/stdc++.h>

using namespace std;

#define gc c=getchar()
#define r(x) read(x)
#define ll unsigned long long

template<typename T>
inline void read(T&x){
    T k=1;char gc;x=0;
    while(!isdigit(c)){if(c=='-')k=-1;gc;}
    while(isdigit(c))x=x*10+c-'0',gc;x*=k;
}

const int p1=1e9+7;
const int p2=998244353;
const int N=200005;
const int INF=0x3f3f3f3f;

int n,m;

struct Info{
    ll v1,v2,v3;
    Info(){}
    Info(int x){
        v1=v2=v3=x;
    }

    inline void operator += (const Info &a){
        if((v1+=a.v1)>=p1)v1-=p1;
        if((v2+=a.v2)>=p2)v2-=p2;
        v3+=a.v3;
    }
};

namespace G1{
    int ecnt;
    int fir[N],nex[N],to[N],dis[N],w[N];
    Info ans[N];

    inline void addedge(int u,int v,int c){
        nex[++ecnt]=fir[u],fir[u]=ecnt,to[ecnt]=v,w[ecnt]=c;
    }

    priority_queue<pair<int,int> >Q;

    inline void dijkstra(int S){
        memset(dis+1,INF,n<<2);
        ans[S]=1;
        dis[S]=0;
        Q.push(make_pair(0,S));
        while(!Q.empty()){
            int x=Q.top().second;
            int d=-Q.top().first;
            Q.pop();
            if(d!=dis[x])continue;
            for(int i=fir[x];i;i=nex[i]){
                int v=to[i];
                if(dis[v]==dis[x]+w[i]){
                    ans[v]+=ans[x];
                }
                if(dis[v]>dis[x]+w[i]){
                    ans[v]=ans[x];
                    dis[v]=dis[x]+w[i];
                    Q.push(make_pair(-dis[v],v));
                }
            }
        }
    }

    inline void work(){
        dijkstra(1);
        if(dis[n]==INF)puts("-1"),exit(0);
    }
}

namespace G2{
    int ecnt;
    int fir[N],nex[N],to[N],dis[N],w[N];
    Info ans[N];

    inline void addedge(int u,int v,int c){
        nex[++ecnt]=fir[u],fir[u]=ecnt,to[ecnt]=v,w[ecnt]=c;
    }

    priority_queue<pair<int,int> >Q;

    inline void dijkstra(int S){
        memset(dis+1,INF,n<<2);
        ans[S]=1;
        dis[S]=0;
        Q.push(make_pair(0,S));
        while(!Q.empty()){
            int x=Q.top().second;
            int d=-Q.top().first;
            Q.pop();
            if(d!=dis[x])continue;
            for(int i=fir[x];i;i=nex[i]){
                int v=to[i];
                if(dis[v]==dis[x]+w[i]){
                    ans[v]+=ans[x];
                }
                if(dis[v]>dis[x]+w[i]){
                    ans[v]=ans[x];
                    dis[v]=dis[x]+w[i];
                    Q.push(make_pair(-dis[v],v));
                }
            }
        }
    }

    inline void work(){
        dijkstra(n);
    }
}

inline bool check(const Info &a,const Info &b,const Info &c){
    if(a.v1*b.v1%p1!=c.v1)return 0;
    if(a.v2*b.v2%p2!=c.v2)return 0;
    if(a.v3*b.v3!=c.v3)return 0;
    return 1;
}

int main(){
    freopen("c.in","r",stdin);
    freopen("c.out","w",stdout);
    r(n),r(m);
    for(int i=1;i<=m;++i){
        int u,v,c;
        r(u),r(v),r(c);
        G1::addedge(u,v,c);
        G2::addedge(v,u,c);
    }
    G1::work();
    G2::work();
    int ans=0;
    for(int i=1;i<=n;++i){
        if(G1::dis[i]+G2::dis[i]==G1::dis[n]&&check(G1::ans[i],G2::ans[i],G1::ans[n])){
            ans++;
        }
    }
    printf("%d\n",ans);
}