线性筛素数……

Program P3006;
const
   maxn=1000000;
var
   prime:array[1..maxn] of boolean;
   p:array[1..maxn] of longint;
   t:longint;
   a,d,n:longint;
Procedure primeing;
var
   i,j:longint;
begin
   fillchar(prime,sizeof(prime),false);
   t:=0;
   prime[1]:=true;
   for i:=2 to maxn do
   begin
      if not(prime[i]) then
      begin
         inc(t);
         p[t]:=i;
      end;
      for j:=1 to t do
      begin
         if p[j]*i>maxn then break;
         prime[p[j]*i]:=true;
         if i mod p[j]=0 then break;
      end;
   end;
end;
begin
   primeing;
   readln(a,d,n);
   while (a+d+n>0) do
   begin
      while (n>0) do
      begin
         if not(prime[a]) then dec(n);
         inc(a,d);
      end;
      writeln(a-d);
      readln(a,d,n);
   end;
end.