#include<bits/stdc++.h>
using namespace std;
 
#define ll long long
#define pb push_back
#define pii pair<int, int>
#define pll pair<ll, ll>
#define vvi vector<vector<int>>
#define vt vector
#define arr array
#define ALL(x) begin(x), end(x)
#define rALL(x) rbegin(x), rend(x)
#define SZ(x) x.size()
const int MOD1=998244353;
const int MOD2=1e9+7;
const ll LINF=1e18;
const int INF=1e9;
 
const int N=2e5+1;
vt<ll> BIT_s(N, -LINF), BIT_g(N, -LINF);
ll n, c, m, t, p, ans=0;
 
void upd_s(int u, ll d){
	for ( ; u<=n; u+=(-u&u)) BIT_s[u]=max(BIT_s[u], d);
}
 
void upd_g(int u, ll d){
	for ( ; u<=n; u+=(-u&u)) BIT_g[u]=max(BIT_g[u], d);
}
 
ll qry_s(int u, ll res=-LINF){
	for ( ; u; u-=(-u&u)) res=max(res, BIT_s[u]);
	return res;
}
 
ll qry_g(int u, ll res=-LINF){
	for ( ; u; u-=(-u&u)) res=max(res, BIT_g[u]);
	return res;
}
 
int main(){
    ios::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
 
    cin>>n>>c>>m;
    upd_s(1, c);
    upd_g(n, -c);
 
    while(m--){
    	cin>>t>>p;
    	// t = current market, i = previous market
 
    	// BIT_s = - c * (t - i) -> - c * t + c * i
    	// come from market with smaller id (BIT_s) = - c * t
 
    	// BIT_g = - c * (i - t) -> - c * i + c * t
    	// come fromt market with larger id (BIT_g) = + c * t
 
    	ll res = max(qry_s(t) - c * t, qry_g(n+1-t) + c * t) + p;
    	ans=max(ans, res);
    	upd_s(t, res + c * t);
    	upd_g(n+1-t, res - c * t);
    }
    cout<<ans<<'\n';
 
    return 0;
}

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50 1000000000
15
30 60541209756
48 49238708511
1 73787345006
24 47221018887
9 20218773368
34 40025202486
14 28286410866
24 82115648680
37 62913240066
14 92020110916
24 20965327730
32 67598565422
39 79828753874
40 52778306283
40 67894622518