#include<cstdio>
#include<deque>
#define ll long long
#define nmax 100010
using namespace std;
deque<ll>Q;
ll n,s,t,c[nmax],k,sol,i;
int main()
{
freopen("branza.in","r",stdin);
freopen("branza.out","w",stdout);
scanf("%lld%lld%lld", &n, &s, &t);
for(i=1;i<=n;++i)
{
scanf("%lld%lld", &c[i], &k);
for(;Q.size()&&(c[Q.back()]+s*(i-Q.back())>c[i]);Q.pop_back());
Q.push_back(i);
if(Q.front()+t<i)Q.pop_front();
sol+=k*(c[Q.front()]+s*(i-Q.front()));
}
printf("%lld", sol);
return 0;
}