first = 1;
     last = 5;
     current = 1;
           
     function nextPicture() {
         // Hide current picture
         object = document.getElementById('slide' + current);
         object.style.display = 'none';
               
         // Show next picture, if last, loop back to front
         if (current == last) { current = 1; }
         else { current++ }
         object = document.getElementById('slide' + current);
         object.style.display = 'block';
		 setTimeout(nextPicture, 5000);
      }

      function previousPicture() {
         // Hide current picture
         object = document.getElementById('slide' + current);
         object.style.display = 'none';
               
         if (current == first) { current = last; }
         else { current--; }
         object = document.getElementById('slide' + current);
         object.style.display = 'block';
     }