#include <bits/stdc++.h>
#pragma GCC optimize ("O2,unroll-loops")
//#pragma GCC optimize("no-stack-protector,fast-math")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<pii, int> piii;
typedef pair<ll, ll> pll;
#define debug(x) cerr<<#x<<'='<<(x)<<endl;
#define debugp(x) cerr<<#x<<"= {"<<(x.first)<<", "<<(x.second)<<"}"<<endl;
#define debug2(x, y) cerr<<"{"<<#x<<", "<<#y<<"} = {"<<(x)<<", "<<(y)<<"}"<<endl;
#define debugv(v) {cerr<<#v<<" : ";for (auto x:v) cerr<<x<<' ';cerr<<endl;}
#define all(x) x.begin(), x.end()
#define pb push_back
#define kill(x) return cout<<x<<'\n', 0;
const int inf=1000000010;
const ll INF=1000000000000001000LL;
const int mod=1000000007;
const int MAXN=200010, LOG=17;
int n, m, k, u, v, x, y, t, a, b, ans;
int A[MAXN], B[MAXN], C[MAXN];
int ps[MAXN], ps2[MAXN];
vector<int> vec[MAXN];
struct Fenwick{
int fen[MAXN];
void reset(){
memset(fen, 0, sizeof(fen));
}
void add(int pos, int val){
for (; pos<MAXN; pos+=pos&-pos) fen[pos]+=val;
}
int get(int pos){
int res=0;
for (; pos; pos-=pos&-pos) res+=fen[pos];
return res;
}
} fen;
bool Check2(int ted){
fen.reset();
fen.add(1, ted);
for (int i=1; i<n; i++) fen.add(i, ps[i]-ps[i-1]);
priority_queue<int> pq;
for (int i=1; i<n; i++){
for (int j:vec[i]) pq.push(j);
while (fen.get(i)>ans){
if (pq.empty() || !(ted--)) return 0;
int j=pq.top();
pq.pop();
if (j<=i) return 0;
fen.add(i, -2);
fen.add(j, +2);
}
}
return 1;
}
bool Check(){
memset(ps, 0, sizeof(ps));
for (int i=1; i<=m; i++){
ps[A[i]]++;
ps[B[i]]--;
}
for (int i=1; i<=n; i++) ps[i]+=ps[i-1];
int mx=*max_element(ps+1, ps+n);
if (mx<=ans) return 1;
if ((mx+1)/2>ans) return 0;
for (int i=1; i<n; i++) if (ps[i]==mx){ // FFS be small
for (int j=1; j<n; j++) vec[j].clear();
for (int j=1; j<=m; j++) if (A[j]<=i && i<B[j]) vec[A[j]].pb(B[j]);
for (int j=mx-ans; j<=ans; j++) if (Check2(j)) return 1;
break ;
}
return 0;
}
int main(){
ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
//freopen("input.txt", "r", stdin);
//freopen("output.txt", "w", stdout);
cin>>n>>m;
for (int i=1; i<=m; i++){
cin>>A[i]>>B[i]>>C[i];
if (A[i]>B[i]) swap(A[i], B[i]);
assert(C[i]==1);
}
int dwn=0, up=m;
while (up-dwn>1){
ans=(dwn+up)>>1;
if (Check()) up=ans;
else dwn=ans;
}
cout<<up<<"\n";
return 0;
}
/*
3 3
1 2 1
2 3 1
3 1 1
6 3
1 4 1
2 5 1
3 6 1
*/
