#include <bits/stdc++.h>
using namespace std;
const int MAXN = 5005;
using pi = pair<int, int>;
int n, m;
int a[MAXN], b[MAXN], c[MAXN];
bool Do(vector<int> l, vector<int> r, vector<pi> intv, int K){
l[0] = r[0] = 1e9;
for(int i=1; i<l.size(); i++) l[i] = min(l[i], l[i - 1]);
for(int i=1; i<r.size(); i++) r[i] = min(r[i], r[i - 1]);
l.push_back(0);
sort(intv.begin(), intv.end());
priority_queue<int, vector<int>, greater<int>> pq;
int ptr = 0;
vector<int> opt(r.size());
for(int i=0; i + 1<l.size(); i++){
while(ptr < intv.size() && intv[ptr].first <= i){
pq.push(intv[ptr++].second);
}
while(l[i + 1] < K){
if(pq.empty()) return 0;
int nxt = pq.top(); pq.pop();
opt[nxt]++;
K--;
}
}
for(int i=opt.size()-2; i>=0; i--) opt[i] += opt[i + 1];
for(int i=0; i<r.size(); i++){
if(opt[i] > r[i]) return false;
}
return true;
}
int cnt[MAXN];
bool trial(int x){
int maxpos = max_element(cnt + 1, cnt + n + 1) - cnt;
int mx = cnt[maxpos];
if(mx <= x) return true;
for(int i=mx-x; i<=mx-x+1 && i<=m; i++){
vector<int> surp(n - 1);
for(int j=0; j<n-1; j++){
surp[j] = x + i - cnt[j + 1];
surp[j] /= 2;
}
// number of reversal
int j = maxpos;
assert(j - 1 < surp.size() && surp[j - 1] == 0);
vector<pi> intv;
for(int k=0; k<m; k++){
if(a[k] <= j && b[k] > j){
intv.emplace_back(a[k] - 1, n - b[k]);
}
}
vector<int> l = {0};
vector<int> r = {0};
for(int k=0; k<j-1; k++) l.push_back(surp[k]);
for(int k=n-2; k>=j; k--) r.push_back(surp[k]);
if(Do(l, r, intv, i)) return true;
}
return false;
}
int main(){
cin >> n >> m;
for(int i=0; i<m; i++){
cin >> a[i] >> b[i] >> c[i];
if(a[i] > b[i]) swap(a[i], b[i]);
cnt[a[i]]++;
cnt[b[i]]--;
}
for(int i=1; i<=n; i++) cnt[i] += cnt[i-1];
int s = 0, e = 10000;
while(s != e){
int m = (s+e)/2;
if(trial(m)) e = m;
else s = m+1;
}
cout << s << endl;
}
