#include<fstream>
using namespace std;
long long i,n,st=1,dr,st,s,v[100010],v1[100010],v2[100010];
int main()
{ifstream q("branza.in");
ofstream w("branza.out");
q>>n>>s>>t;
for(int i=1;i<=n;++i)
  q>>v[i]>>v1[i];
for(i=1;i<=n;++i)
  {while(st<=dr&&v[i]<v[v2[dr]]+s*(i-v2[dr]))
      --dr;
  v2[++dr]=i;
  if(v2[st]==i-t-1)
   ++st;
  s=s+(v[v2[st]]+(i-v2[st])*s);}
w<<s<<"\n";
return 0;}