fix signed vs. unsigned warning
diff --git a/apps/s_server.c b/apps/s_server.c
index aeec035..72d0b6c 100644
--- a/apps/s_server.c
+++ b/apps/s_server.c
@@ -889,7 +889,7 @@
                         }
                 else if (strcmp(*argv,"-psk") == 0)
 			{
-			int i;
+			size_t i;
 
 			if (--argc < 1) goto bad;
 			psk_key=*(++argv);