#include<cstdio>
#include<algorithm>
int n,m,i,j,d[400086];
int ans[400086],f[400086][20],de[400086];
struct road{
    int f,t,w;
    bool b;
}a[200086];
int gd(int g){
    if(d[g]==g)return g;
    return d[g]=gd(d[g]);
}
bool cmp(road a,road b){
    return a.w<b.w;
}
int main(){
    scanf("%d%d",&n,&m);
    for(i=0;i<m;++i){
        scanf("%d%d%d",&a[i].f,&a[i].t,&a[i].w);
        --a[i].f;
        --a[i].t;
    }std::sort(a,a+m,cmp);
    for(i=0;i<n;++i)d[i]=i;
    for(i=0;i<m;++i)if(gd(a[i].f)!=gd(a[i].t)){
        a[i].b=1;
        d[gd(a[i].f)]=gd(a[i].t);
    }
    for(i=0;i<n+n;++i)d[i]=i;
    int K=n;
    for(i=0;i<m;++i)if(!a[i].b)if(gd(a[i].f)!=gd(a[i].t)){
        f[gd(a[i].f)][0]=f[gd(a[i].t)][0]=K;
        d[gd(a[i].f)]=d[gd(a[i].t)]=K;
        ans[K]=a[i].w;
        ++K;
    }
    if(K<n+n-1){
        puts("-1");
        return 0;
    }
    f[K-1][0]=K-1;
    de[K-1]=0;
    for(i=K-1;~i;--i){
        de[i]=de[f[i][0]]+1;
        for(j=0;j<19;++j)f[i][j+1]=f[f[i][j]][j];
    }
    long long A=0;
    for(i=0;i<m;++i)if(a[i].b){
        int u=a[i].f,v=a[i].t;
        for(j=19;~j;--j)if(de[u]>=de[v]+(1<<j))u=f[u][j];
        for(j=19;~j;--j)if(de[v]>=de[u]+(1<<j))v=f[v][j];
        for(j=19;~j;--j)if(f[u][j]!=f[v][j])u=f[u][j],v=f[v][j];
        A+=ans[f[u][0]]+1-a[i].w;
    }printf("%lld",A);
    return 0;
}