#include <fstream>

using namespace std;
ifstream fin("branza.in");
ofstream fout("branza.out");
const int N=100001;
int v[N],d[N],c[N];
int main()
{
    int n,x,k,st,dr,p,i;
    long long s=0;
    fin>>n>>x>>k;
    k++;
    st=0;
    dr=-1;
    for(i=0; i<n; i++)
    {
        fin>>c[i]>>p;
        if(st<=dr && d[st]==i-k) st++;
        while(st<=dr && c[i]<=c[d[dr]]+x*(i-d[dr]))
            dr--;
        d[++dr]=i;
        s += (c[d[st]]+(long long)x*(i-d[st]))*p;
    }
    fout<<s;
    return 0;
}