#include <bits/stdc++.h>
using namespace std;
#define int              long long int
#define double           long double
#define print(a)         for(auto x : a) cout << x << " "; cout << endl


const int M = 1000000007;
const int N = 3e5+9;
const int INF = 2e9+1;
const int LINF = 2000000000000000001;

inline int power(int a, int b, int mod=M) {
    int x = 1;
    a %= mod;
    while (b) {
        if (b & 1) x = (x * a) % mod; 
        a = (a * a) % mod;
        b >>= 1;
    }
    return x;
}


//_ ***************************** START Below *******************************

// 3
// 2 10
// 1 8
// 4 9
// 6 7



vector<vector<int>> a;

int consistency(int n, int rate, int capacity){
	
	sort(begin(a), end(a));
	
	int balance = 0;
	int ans = 0;
	
	for(int i=0; i<n; i++){
		int t = a[i][0];
		int pkt = a[i][1];
		
		if(i-1>=0){
			int lastT = a[i-1][0];
			int timeDif = t-lastT;
			
			balance = max(0LL, balance - rate*timeDif);  
		}
		
		balance += pkt;
		
		if(balance > capacity){
			ans += balance - capacity;
			balance = capacity;
		}
		
		
	}
	
	return ans;
}















int practice(int n, int rate, int capacity){


    return 0;
}





void solve() {
    
    int n;
    cin>> n;
    int capacity, rate;
    cin >> rate >> capacity;
    
    a.resize(n);
    for(int i=0; i<n; i++){
    	int x, y;
    	cin >> x >> y;
    	a[i] = {x, y};
    }
    
    cout << consistency(n, rate, capacity) << endl;


}





int32_t main() {
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

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

    return 0;
}