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

using ll = long long;
using pll = pair<ll,ll>;
using vll = vector<ll>;
using vi = vector<int>;
using pi = pair<int, int>;
using vpi = vector<pair<int, int>>;
using vai = vector<array<int, 3>>;

#define x first
#define y second
#define all(x) x.begin(), x.end()

void solve() {
    int n, m; cin >> n >> m;
    vpi v(n);
    for (int i = 1; i <= m; i++) {
        int a, b; cin >> a >> b;
        a--;
        if (v[a].x < b) {
            v[a].x = b;
            v[a].y = i;
        }
    }

    //for (pi p : v) cout << p.x << " " << p.y << "\n";

    vi dp(n);
    int best=0;
    for (int i = 0; i < n; i++) {
        dp[i] = best+v[i].x;
        if (i > 0) {
            best = max(best, dp[i-1]);
        } //cout << best << " ";
    } //cout << "\n"; 
    //for (int i : dp) cout << i << " ";
    cout << dp[n-1];
}

int main() {
	ios::sync_with_stdio(0);
    cin.tie(0);

    int t=1;
    //cin >> t;
    while (t--) {
        solve();
    }
}