using P=pair<ll,pair<ll,ll>>;
P a[2d5];
ll s[2d5];
ll z[2d5];
{
	ll@n,@q;
	rep(i,q){
		ll@l,@r,@b;
		a[i]={-b,{r,l-1}};
	}
	sortA(q,a);
	ll fb=0,fi=0;
	rep(i,q){
		ll b=-a[i].first;
		ll l=a[i].second.second;
		ll r=a[i].second.first;
		ll f=(fb==b&&fi>=l);
		while(1){
			ll t=l;
			while(t<r&&s[t]){
				t=s[t];
			}
			if(t>=r){
				if(l!=t){
					s[l]=t;
				}
				break;
			}
			f=1;
			l=t;
			s[l]=l+1;
			z[l]=b;
			if(!(fb==b&&fi>=l)){
				fb=b;
				fi=l;
			}
		}
		if(!f){
			wt(-1);
			exit(0);
		}
	}
	rep(i,n){
		if(!z[i]){
			z[i]=1;
		}
	}
	wt(z(n));
}