#include <cstdio>

#define NMAX 100007
#define LL long long

using namespace std;
int n, s, t, dq[NMAX], st = 1, dr = 1;
LL v[NMAX], p, ans;

int main()
{
    freopen("branza.in", "r", stdin);
    freopen("branza.out", "w", stdout);
    scanf("%d%d%d%lld%lld", &n, &s, &t, &v[1], &p);
    dq[1] = 1;
    ans = v[1]*p;
    //printf("%lld %lld %lld\n", ans, v[1], p);
    for(int i = 2; i<= n; ++i)
    {
        //printf("i = %d st = %d dr = %d dq[st] = %d dq[dr] = %d\n", i, st, dr, dq[st], dq[dr]);
        scanf("%lld %lld", &v[i], &p);
        while(dr >= st && v[i] <= v[dq[dr]] + s*(i - dq[dr])) dr--;
        dr++;
        //printf("dr = %d\n", dr);
        dq[dr] = i;
        //printf("st = %d dr = %d dq[st] = %d dq[dr] = %d\n", st, dr, dq[st], dq[dr]);
        //printf("check %lld\n", (v[dq[st]]+s*(i - dq[st]))*p);
        ans += (v[dq[st]]+s*(i - dq[st]))*p;
        //printf("ans = %lld\n", ans);
        if(dq[st] + t <= i) st++;
    }
    printf("%lld\n", ans);
    return 0;
}