#include <cstdio>
long long n , s , t , v[100001] , d[100001] , p = 1 , q , c , sol;
int main()
{
  freopen("branza.in" , "r" , stdin);
  freopen("branza.out" , "w" , stdin);
  scanf("%lld%lld%lld" , &n , &s , &t);
    for(int i = 1; i <= n; ++ i)
    {
        scanf("%lld%lld" , &v[i] , &c);
        while(s * (i - d[ q ] ) + v[ d [ q ] ] >= v[ i ] && p <= q)
          -- q;
        ++ q;
        d[ q ] = i;
        if(i -d[ p ] > t)
          ++p;
        sol += c * ( s * (i - d[p] ) + v[d[ p ]]);
    }
    printf("%lld" , sol);
    return 0;
}