#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=100010, 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> vec2[MAXN];
bool Check2(vector<pii> &vec, int ted){
for (int i=1; i<n; i++) vec2[i].clear(), ps2[i]=ps[i]+ted;
for (pii p:vec) vec2[p.first].pb(p.second);
priority_queue<int/*, vector<int>, greater<int>*/> pq;
for (int i=1; i<n; i++){
for (int j:vec2[i]) pq.push(j);
while (ps2[i]>ans){
if (pq.empty() || !(ted--)) return 0;
int j=pq.top();
if (j<i) return 0;
while (j>i) ps2[--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];
// cerr<<"ps: ";for (int i=1; i<=n; i++) cerr<<ps[i]<<" \n"[i==n];
int mx=*max_element(ps+1, ps+n);
if (mx<=ans) return 1; // useless TOF
for (int i=1; i<n; i++) if (ps[i]==mx){ // FFS be small
vector<pii> vec;
for (int j=1; j<=m; j++) if (A[j]<=i && i<B[j]) vec.pb({A[j], B[j]});
for (int j=1; j<=vec.size() && j<=ans; j++) if (Check2(vec, j)) return 1;
}
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
*/
