#include <stdio.h>
#define N 100000
int kg[N],c[N],d[N];
int main()
{
    FILE *f1 = fopen("branza.in","r"),*f2 = fopen("branza.out","w");
    int n,s,t,dr,st,i;
    long long sum;
    fscanf(f1,"%d%d%d",&n,&s,&t);
    t++;
    sum = 0;
    st = 0;
    dr = -1;
    for(i=0;i<n;i++){
        fscanf(f1,"%d%d",&c[i],&kg[i]);
        while(st<=dr && d[st] == i-t)
            st++;
        while(st<=dr && c[i] <= c[d[dr]] + s*(i-d[dr])){
            dr--;
        }
        d[++dr] = i;
        sum +=(long long) (c[d[st]] + s*(i-d[st]))* kg[i];
    }
    fprintf(f2,"%lld",sum);
    return 0;
}