{
N - numarul de oi
X - distanta maxima de la care lupul poate alege oi
L - distanta cu care se departeaza oile de lup dupa fiecare alegere

D[] - distanta initiala
A[] - cantitatea de lana
}

program lupu;
type
        sir=array[0..100000] of longint;
var
        f:text;
        d,a,t,h:sir;
        j,n,x,l,i,k,tmax,c:longint;
        heap:sir;
        suma:int64;

function partitie(first,last:longint):longint;
var
        q,i,j,aux:longint;
begin
        q:=t[first];
        i:=first-1;
        j:=last+1;
        while true do begin
                repeat inc(i); until t[i]<=q;
                repeat dec(j); until t[j]>=q;
                if i<j then begin
                        aux:=t[i]; t[i]:=t[j]; t[j]:=aux;
                        aux:=a[i]; a[i]:=a[j]; a[j]:=aux;
                        aux:=d[i]; d[i]:=d[j]; d[j]:=aux;
                end
                else begin
                        partitie:=j;
                        exit;
                end;
        end;
end;


procedure qs(first,last:longint);
var
        q:longint;
begin
        if first<last then begin
                q:=partitie(first,last);
                qs(first,q);
                qs(q+1,last);
        end;
end;

function partitie1(first,last:longint):longint;
var
        q,aux,i,j:longint;
begin
        q:=h[first];
        i:=first-1;
        j:=last+1;
        while true do begin
                repeat inc(i); until h[i]>=q;
                repeat dec(j); until h[j]<=q;
                if i<j then begin
                        aux:=h[i]; h[i]:=h[j]; h[j]:=aux;
                end
                else begin
                        partitie1:=j;
                        exit;
                end;
        end;
end;

procedure qs1(first,last:longint);
var
        q:longint;
begin
        if first<last then begin
                q:=partitie1(first,last);
                qs1(first,q);
                qs1(q+1,last);
        end;
end;

begin
        assign(f,'lupu.in');
        reset(f);
        readln(f,n,x,l);
        for i:=1 to n do begin
            readln(f,d[i],a[i]);
            if d[i]>x then t[i]:=0
            else t[i]:=1+(x-d[i]) div l;
            if t[i]>tmax then tmax:=t[i];
        end;
        close(f);
        qs(1,n);
        suma:=0;
        j:=1;
        c:=0;
        for i:=tmax downto 1 do begin
            while t[j]=i do begin
                inc(c);
                h[c]:=a[j];
                inc(j);
            end;
            qs1(1,c);
            suma:=suma+h[c];
            dec(c);
        end;
        assign(f,'lupu.out');
        rewrite(f);
        writeln(f,suma);
        close(f);
end.