#include <bits/stdc++.h>
#define ll long long
#define fi first
#define se second
#define el '\n'
#define pback push_back
#define pii pair <int, int>
#define plli pair <ll, int>
#define pill pair <int, ll>
#define pllll pair <ll, ll>
#define FOR(i, a, b) for (int i = a; i <= b; ++i)
#define FORD(i, a, b) for (int i = a; i >= b; --i)

using namespace std;

const int N = 2e5 + 5;
const ll MOD = 1e9 + 7;
const ll MOD1 = 998244353;
const int MASK = (1 << 20);
const int base = 256;
const int BL = 447;

int n, q;
ll f[N], g[N];

void input() {
    cin >> n >> q;
    while (q--) {
        int l, r;
        cin >> l >> r;
        f[l]++;
        f[r + 1]--;
        //
        g[l] += 1 - l;
        g[r + 1] -= (1 - l);
    }
    ll res = 0;
    FOR(i, 1, n) {
        f[i] += f[i - 1];
        g[i] += g[i - 1];
        ll val = 1ll * f[i] * i + g[i];
        res = max(res, val);
    }
    cout << res;
}

signed main()
{
    #define name "task"
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    if (fopen(name".inp", "r")) {
        freopen(name".inp", "r", stdin);
        freopen(name".ans", "w", stdout);
    }
    //
    input();
    //cerr << "Time elapsed: " << (1.0 * clock() / CLOCKS_PER_SEC) << "s";
    return 0;
}