#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pll pair<ll, ll>
#define pii pair<int, int>
#define fs first
#define sc second
#define pb push_back
void solve() {
int n,q;
cin>>n>>q;
vector<pii> seg[n];
while(q--){
int l,r,x;
cin>>l>>r>>x;
seg[l].pb({r,x});
}
int a[n];
priority_queue<pii> pq;
for(int i=0;i<n;i++){
for(auto[r,x]:seg[i]){
pq.push({x,r});
}
while(!pq.empty()&&pq.top().sc<i)pq.pop();
if(pq.empty())a[i]=-1;
else a[i]=pq.top().fs;
}
auto imp=[&]{
while(n--)cout<<"-1 ";
cout<<'\n';
exit(0);
};
vector<int> idx[n];
for(int i=0;i<n;i++){
if(a[i]>=0)idx[a[i]].pb(i);
}
memset(a,-1,sizeof(a));
pii rg[n];
for(int i=0;i<n;i++)rg[i]={0,n-1};
for(int i=0;i<n;i++){
for(auto[r,x]:seg[i]){
rg[x].fs=max(rg[x].fs,i);
rg[x].sc=min(rg[x].sc,r);
}
}
bool vis[n];
memset(vis,0,sizeof(vis));
for(int i=0;i<n;i++){
for(int j:idx[i]){
if(rg[i].fs<=j&&j<=rg[i].sc){
a[j]=i;
vis[i]=1;
break;
}
}
}
int v=0;
for(int i=0;i<n;i++){
v=max(v,i);
for(int j:idx[i])if(a[j]==-1){
while(v<n&&vis[v])v++;
if(v==n)imp();
vis[v]=1;
a[j]=v;
}
}
v=0;
for(int i=0;i<n;i++)if(a[i]==-1){
while(vis[v])v++;
a[i]=v;
vis[v]=1;
}
int sp[n][20];
for(int i=0;i<n;i++)sp[i][0]=a[i];
for(int x=1;x<20;x++){
for(int i=0;i+(1<<x)<=n;i++)sp[i][x]=min(sp[i][x-1],sp[i+(1<<x-1)][x-1]);
}
for(int i=0;i<n;i++){
for(auto[r,x]:seg[i]){
int k=31-__builtin_clz(r-i+1);
if(min(sp[i][k],sp[r-(1<<k)+1][k])!=x){
imp();
}
}
}
for(int i=0;i<n;i++)cout<<a[i]<<' ';
cout<<'\n';
}
int main() {
#ifdef FPO
freopen("in","r",stdin);
freopen("out","w",stdout);
#endif
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
solve();
}
