#include<bits/stdc++.h>
#define int long long
#define mod 998244353ll
#define pii pair<int,int>
#define fi first
#define se second
#define mems(x,y) memset(x,y,sizeof(x))
#define pb push_back
#define db double
using namespace std;
const int maxn=300010;
const int inf=1e18;
inline int read(){
	int x=0,f=1;
	char ch=getchar();
	while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
	while(ch>='0'&&ch<='9'){x=(x<<3)+(x<<1)+(ch-48);ch=getchar();}
	return x*f;
}
bool Mbe;

int n,m,ans;
struct edge{
	int u,v,w;
}g[maxn];
int f[maxn],siz[maxn];
int fd(int x){
	if(f[x]==x)return x;
	return f[x]=fd(f[x]);
}
bool vis[maxn];
int head[maxn],tot;
struct nd{
	int nxt,to,w;
}e[maxn<<1];
void add(int u,int v,int w){e[++tot]={head[u],v,w};head[u]=tot;}
int to[maxn][19],w[maxn][19],dep[maxn];
int calc(int u,int v){
	int res=inf;
	if(dep[u]<dep[v])swap(u,v);
	for(int i=18;~i;i--)if(dep[to[u][i]]>=dep[v])res=min(res,w[u][i]),u=to[u][i];
	if(u==v)return res;
	for(int i=18;~i;i--)if(to[u][i]!=to[v][i])u=to[u][i],v=to[v][i],res=min({res,w[u][i],w[v][i]});
	return min({res,w[u][0],w[v][0]});
}
void dfs(int u){
	dep[u]=dep[to[u][0]]+1;
	for(int i=1;i<=18;i++)to[u][i]=to[to[u][i-1]][i-1],w[u][i]=min(w[u][i-1],w[to[u][i-1]][i-1]);
	for(int i=head[u];i;i=e[i].nxt){
		int v=e[i].to;if(v==to[u][0])continue;
		to[v][0]=u,w[v][0]=e[i].w;dfs(v);
	}
}
void work(){
	n=read();m=read();
	for(int i=1;i<=m;i++)g[i]={read(),read(),read()};
	for(int i=1;i<=n;i++)f[i]=i,siz[i]=1;
	sort(g+1,g+m+1,[&](edge u,edge v){return u.w>v.w;});
	for(int i=1;i<=m;i++){
		int u=g[i].u,v=g[i].v;
		if(fd(u)!=fd(v)){
			add(u,v,g[i].w),add(v,u,g[i].w);
			u=fd(u),v=fd(v);
			(ans+=siz[u]*siz[v]%mod*g[i].w)%=mod;
			// cout<<siz[u]<<" "<<siz[v]<<" "<<g[i].w<<"\n";
			f[v]=u,siz[u]+=siz[v];
			vis[i]=1;
		}
	}
	int sum=n*(n-1)/2;
	for(int i=1;i<=n;i++)if(f[i]==i)sum-=siz[i]*(siz[i]-1)/2;
	ans+=sum;
	dfs(1);
	for(int i=1;i<=m;i++)if(!vis[i]){
		if(calc(g[i].u,g[i].v)!=g[i].w){puts("-1");return ;}
	}
	printf("%lld\n",ans);
}

// \
444

bool Med;
int T;
signed main(){
//	freopen(".in","r",stdin);
//	freopen(".out","w",stdout);
	
//	ios::sync_with_stdio(0);
//	cin.tie(0);cout.tie(0);
	
//	cerr<<(&Mbe-&Med)/1048576.0<<" MB\n";
	
	T=1;
	while(T--)work();
}