#include <fstream>
#include <vector>
#include <deque>

using namespace std;

class InParser {
private:
	FILE *fin;
	char *buff;
	int sp;

	char read_ch() {
		++sp;
		if (sp == 4096) {
			sp = 0;
			fread(buff, 1, 4096, fin);
		}
		return buff[sp];
	}

public:
	InParser(const char* nume) {
		fin = fopen(nume, "r");
		buff = new char[4096]();
		sp = 4095;
	}
	
	InParser& operator >> (int &n) {
		char c;
		while (!isdigit(c = read_ch()) && c != '-');
		int sgn = 1;
		if (c == '-') {
			n = 0;
			sgn = -1;
		} else {
			n = c - '0';
		}
		while (isdigit(c = read_ch())) {
			n = 10 * n + c - '0';
		}
		n *= sgn;
		return *this;
	}
	
	InParser& operator >> (long long &n) {
		char c;
		n = 0;
		while (!isdigit(c = read_ch()) && c != '-');
		long long sgn = 1;
		if (c == '-') {
			n = 0;
			sgn = -1;
		} else {
			n = c - '0';
		}
		while (isdigit(c = read_ch())) {
			n = 10 * n + c - '0';
		}
		n *= sgn;
		return *this;
	}
};

InParser cin("branza.in");
ofstream cout("branza.out");

#define int long long

struct Info {
    int price;
    int to_beBought;
};

struct InfoDeque {
    int val;
    int idx;
    InfoDeque() {}
    InfoDeque(int val,int idx) {
        this->val = val;
        this->idx = idx;
    }
};

int n,price_toKeepPerKg,maxPeriodToKeep;
vector<Info> v;

void read() {
    cin>>n>>price_toKeepPerKg>>maxPeriodToKeep;
    v.resize(n+1);
    for(int i=1;i<=n;i++) {
        cin>>v[i].price>>v[i].to_beBought;
    }
}

void solve() {
    deque<InfoDeque> dq;
    vector<int> dp(n+1);
    for(int i=1;i<=n;i++) {
        while(!dq.empty() && dq.back().val >= v[i].price + (n-i+1) * price_toKeepPerKg) {
            dq.pop_back();
        }
        while(!dq.empty() && dq.front().idx < i-maxPeriodToKeep) {
            dq.pop_front();
        }
        dq.push_back((*new InfoDeque(v[i].price + (n-i+1) * price_toKeepPerKg, i)));
        dp[i] = min(v[i].price, v[dq.front().idx].price + ((i-dq.front().idx) * price_toKeepPerKg));
    }
    int rs=0;
    for(int i=1;i<=n;i++) {
        rs+=dp[i] * v[i].to_beBought;
    }
    cout<<rs;
}

int32_t main() {

    read();
    solve();
    return 0;
}