diff --git a/.gitignore b/.gitignore
index 4527a96..cc22819 100644
--- a/.gitignore
+++ b/.gitignore
@@ -19,6 +19,7 @@ user/usys.S
 xv6.out*
 .vagrant/
 submissions/
+mkfs/mkfs
 ph
 barrier
 /lab-*.json
diff --git a/Makefile b/Makefile
index 77ecadc..b7593a7 100644
--- a/Makefile
+++ b/Makefile
@@ -190,6 +190,7 @@ UPROGS=\
 	$U/_zombie\
 	$U/_sleep\
 	$U/_pingpong\
+	$U/_primes\
 
 
 
diff --git a/mkfs/mkfs b/mkfs/mkfs
old mode 100644
new mode 100755
index f849fd5..7a0d222
Binary files a/mkfs/mkfs and b/mkfs/mkfs differ
diff --git a/user/primes.c b/user/primes.c
new file mode 100644
index 0000000..d65494e
--- /dev/null
+++ b/user/primes.c
@@ -0,0 +1,61 @@
+#include "kernel/types.h"
+#include "user/user.h"
+
+void redirect(int n, int pd[]) {
+    close(n);
+    dup(pd[n]);
+    close(pd[0]);
+    close(pd[1]);
+}
+
+void primes() {
+    int previous, next;
+    int fd[2];
+
+    while (read(0, &previous, sizeof(int))) {
+        printf("prime %d\n", previous);
+
+        if (pipe(fd) < 0) {
+            fprintf(2, "pipe failed\n");
+            exit(1);
+        }
+
+        if (fork() == 0) {
+            redirect(1, fd);
+            while (read(0, &next, sizeof(int))) {
+                if (next % previous != 0) {
+                    write(1, &next, sizeof(int));
+                }
+            }
+            exit(0);
+        } else {
+            close(fd[1]);
+            redirect(0, fd);
+        }
+    }
+}
+
+int main(int argc, char *argv[]) {
+    int fd[2];
+
+    if (pipe(fd) < 0) {
+        fprintf(2, "pipe failed\n");
+        exit(1);
+    }
+
+    if (fork() == 0) {
+        redirect(1, fd);
+        for (int i = 2; i < 36; i++) {
+            write(1, &i, sizeof(int));
+        }
+        exit(0);
+    } else {
+        close(fd[1]);
+        redirect(0, fd);
+        primes();
+    }
+
+    exit(0);
+}
+
+