#include<bits/stdc++.h>
using namespace std;
#define il inline
#define ll long long
#define rg register
#define gc getchar()
#define t(i) edge[i].to
#define rp(i,x,y) for(rg int i=x;i<=y;++i)
#define my(i,x,y) for(rg int i=x;i>=y;--i)
#define e(i,x) for(rg int i=head[x];i;i=edge[i].nxt)

+,M=+;
int n,m,ed_cnt,nw_ed_cnt,fa[N],dfn[N],low[N],head[N],tim,in[N];
];
struct eded{int fr,to,wei;}nwed[N];

il int read()
{
    rg ;rg ;
    '))ch=gc;
    ;
    )+(x<<)+(ch^'),ch=gc;
    return y?x:-x;
}
il void ad(int x,int y,int z){edge[++ed_cnt]=(ed){x,head[y],z};head[y]=ed_cnt;}
void tarjan(int x,int fat)
{
    fa[x]=fat;dfn[x]=low[x]=++tim;
    e(i,x){if(t(i)^fat)if(!dfn[t(i)])tarjan(t(i),x),low[x]=min(low[x],low[t(i)]);else low[i]=min(low[i],dfn[t(i)]);}
}
il bool cmp(eded gd,eded gs){return gd.wei<gs.wei;}

int main()
{
    freopen("yylhq.in","r",stdin);freopen("yylhq.out","w",stdout);
    n=read();m=read();rp(i,,m){int x=read(),y=read(),z=read();ad(x,y,z);ad(y,x,z);}
    rp(i,,n));
    rp(i,,n)e(j,i)if(low[i]==dfn[i] && dfn[t(j)]>dfn[i])nwed[++nw_ed_cnt]=(eded){i,t(j),edge[j].wei};
    sort(nwed+,nwed++nw_ed_cnt,cmp);
    rp(i,,nw_ed_cnt){++ || );}
    printf("-1\n");
    ;
}
/*
    www我判断是WA的,,,有时间再改趴我懒得打辣明天放正确代码趴QAQ
*/