#include <bits/stdc++.h>
using namespace std;
#define FOR(i, a, b) for(int i = (a); i <= (b); ++i)
#define FORD(i, a, b) for(int i = (a); i >= (b); --i)
#define sz(a) (int)(a).size()
#define all(a) (a).begin(), (a).end()
#define bit(s, i) (((s) >> (i)) & 1)
#define ii pair <int, int>
#define fi first
#define se second
#define ll long long
#define eb emplace_back
#define pb push_back
#define __builtin_popcount __builtin_popcountll
template <class X, class Y>
bool maximize(X &x, Y y) {
if(x < y) {
x = y;
return true;
}
return false;
}
template <class X, class Y>
bool minimize(X &x, Y y) {
if(x > y) {
x = y;
return true;
}
return false;
}
void solve();
int32_t main() {
#define task "test"
if(fopen(task".inp", "r")){
freopen(task".inp", "r", stdin);
freopen(task".out", "w", stdout);
}
cin.tie(0)->sync_with_stdio(0);
int tc = 1; // cin >> tc;
FOR(i, 1, tc){
solve();
}
}
const int N=200005;
int n,m,p,a[N],pre[N],f[N]; ll add;
vector<int> seg[N];
bool chk(int x, int y){
FOR(i,1,n) f[i]=0;
int val=a[p]-(x-y);
FOR(i,1,n) pre[i]=max(0,(a[i]+val-x+1)/2);
priority_queue<ii> pq;
int cur=0;
FOR(l,1,p){
for(int r:seg[l]) pq.emplace(r,l);
while(cur<pre[l]){
if(pq.empty()) break;
auto [rs,ls]=pq.top(); pq.pop();
f[ls]++; f[rs+1]--;
}
}
if(pre[x]!=val) return false;
FOR(i,1,n){
f[i]+=f[i-1];
if(f[i]<pre[i]) return false;
}
return true;
}
void solve() {
cin>>n>>m;
FOR(i,1,m){
int l,r,c; cin>>l>>r>>c;
if(l>r) swap(l,r);
if(c&1){
seg[l].eb(r);
a[l]++; a[r+1]--;
}
add+=c/2;
}
p=1;
FOR(i,1,n){
a[i]+=a[i-1];
if(a[i]>a[p]) p=i;
}
int L=0, R=n, res=-1;
while(L<=R){
int M=(L+R)>>1;
if(chk(M,0)||chk(M,1)){
res=M;
R=M-1;
}
else{
L=M+1;
}
}
cout<<res+add<<'\n';
}
