#include<stdio.h>
int N,T,S,v[100010],v1[100010],dq[100010],st,dr,Suma;
int main()
{
freopen("branza.in","r",stdin);
//freopen("branza.out","w",stdout);

scanf("%d %d %d",&N,&S,&T);
for(int i=1;i<=N;++i)
scanf("%d %d",&v[i],&v1[i]);

st=1;
dr=0;
for(int i=1;i<=N;++i)
{
while(st<=dr&&v[i]<v[dq[dr]]+S*(i-dq[dr]))
--dr;
dq[++dr]=i;

if(dq[st]==i-T)
++st;
Suma=Suma+(v[dq[st]]+(i-dq[st])*S)*v1[i];

}

printf("%d\n",Suma);

return 0;
}