#include<bits/stdc++.h>
using namespace std;

//#pragma gcc optimize("Ofast,unroll-loops")
//#pragma gcc target("sse,sse2,sse3,ssse3,sse4,avx,avx2,fma,abm,mmx,popcnt,tune=native")
//#define int long long
//#define double long double
#define MP make_pair
#define F first
#define S second
#define MOD 43200000000000

signed main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);

    int N, K;
    cin >> N >> K;

    vector<int> c(K), d(K);
    for (int i = 0; i < K; i++)
        cin >> c[i] >> d[i];

    vector<long long> dp1(K);
    for (int i = K - 1; i >= 0; i--)
        if (i == K - 1 || c[i] > c[i + 1] || d[i] > d[i + 1])
            dp1[i] = d[i];
        else
            dp1[i] = dp1[i + 1] + 1;

    vector<long long> dp2(K);
    for (int i = K - 1; i >= 0; i--)
        if (i == K - 1 || c[i] > c[i + 1])
            dp2[i] = dp1[i] * (dp1[i] + 1) / 2;
        else if (d[i] <= d[i + 1])
            dp2[i] = (dp1[i + 1] + 1) * d[i];
        else
            dp2[i] = (dp1[i + 1] + 1) * d[i + 1] + (long long)(d[i] + d[i + 1] + 1) * (d[i] - d[i + 1]) / 2;

    long long ans = 0;
    for (long long i : dp2)
        ans += i;
    cout << ans << '\n';

    return 0;
}

//      *   *  *****  *   *  *   *   ****  ****    ****     **    **
//     *   *  *      **  *  *   *  *      *   *  *        * *   * *
//    *****  *****  * * *  *   *  *      ****   *       *  *     *
//   *   *      *  *  **  *   *  *      *  *   *       *****    *
//  *   *  *****  *   *   ***    ****  *   *    ****     *   *****

//      *****  *****  *   *  *      *****  *   *  *****  *****
//        *   *   *  *   *  *        *    **  *    *    *   *
//       *   *   *  *****  *        *    * * *    *    *****
//   *  *   *   *    *    *        *    *  **    *    *
//  ****   *****    *    *****  *****  *   *    *    *