//horatiu11
# include <cstdio>
# include <cstring>
# include <algorithm>
# define nmax 100001
using namespace std;
int n,x,l,H[nmax],d,s,Max,val;
struct oaie{int l,t;}o[nmax];
inline bool cmp(oaie a, oaie b)
{
    return (a.t<b.t);
}
int main()
{
    int i;
    freopen("lupu.in","r",stdin);
    freopen("lupu.out","w",stdout);
    scanf("%d%d%d",&n,&x,&l);
    for(i=1;i<=n;++i)
    {
        scanf("%d%d",&d,&o[i].l);
        if(d<=x)o[i].t=(x-d)/l+1;
    }
    sort(o+1,o+n+1,cmp);
    i=1;val=o[i].t;
    while(i<=n+1)
    {
        if(val==o[i].t)
            Max=max(Max,o[i].l);
        else s+=Max,Max=o[i].l,val=o[i].t;
        ++i;
    }
    printf("%d\n",s);
    return 0;
}