#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;
}
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