#include <fstream>
#define nmax 100005
#define mx 1e+12

using namespace std;

ifstream fin("branza.in");
ofstream fout("branza.out");

int n,dq[nmax],i,k,t,ct,c[nmax],st=1,fn,minn;
long long s;

inline void stanga()
{
    while(st<=fn && c[dq[fn]] >= c[i])
        fn--;
    dq[++fn]=i;
}

int main()
{
    fin>>n>>k>>t;
    for(i=1;i<=n;i++)
    {
        fin>>c[i]>>ct;
        stanga();
        if(dq[st]==i-t-1)
            st++;
        minn=mx;
        for(int j=st;j<=fn;j++)
            minn=min((c[dq[j]]+(i-dq[j])*k),minn);
        s+=ct*min(minn,c[i]);
    }
    fout<<s;
    return 0;
}