var dq,c:array[1..100000] of int64;
n,i,s,t,p,st,dr,sol:int64;
f,g:text;
begin
assign(f,'branza.in');
assign(g,'branza.out');
reset(f);rewrite(g);
readln(f,n,s,t);
st:=1;
i:=1;
while i<=n do
    begin
    readln(f,c[i],p);
    while (st<=dr) and (c[i]+s*(n-i+1)<=c[dq[dr]]+s*(n-dq[dr]+1)) do
          dec(dr);
    inc(dr);
    dq[dr]:=i;
    inc(sol,(c[dq[st]]+s*(i-dq[st]))*p);
    if (i>t) and (dq[st]=i-t) then
       inc(st);
    inc(i);
    end;
write(g,sol);
close(f);close(g);
end.