database=new Array("mar_alg.html","mark_pass.html","marw_ships.html","marw_ships2.html","marwl_D.html","marwl_D2.html","marwl_D3.html","marwl_DB.html","marwl_F.html","marwl_GB.html","marwl_USA.html");

NumberOfFiles=database.length;
StringA=window.location.href;
LengthA=StringA.length;
A=StringA.lastIndexOf("/")+1;
ThisFilename=StringA.substring(A,LengthA);
n=NumberOfFiles-1;

for (var z=0;z<=n;z++)
{
if (database[z]==ThisFilename)
{
ThisPageNumber=z;
}
}
function goBack(){
if (ThisPageNumber-1<0)
{
alert("You are at the beginning of the series");
}
else
{window.location=database[ThisPageNumber-1];
}
}
function goForward(){
if (ThisPageNumber+1>n)
{
alert("You are at the end of the series");
}
else
{window.location=database[ThisPageNumber+1];}}