diff --git a/TODO.md b/TODO.md
index 9996303..f065214 100644
--- a/TODO.md
+++ b/TODO.md
@@ -14,9 +14,24 @@
   - [x] sorting
   - [x] writing runs
 - [ ] stage 2
-  - [ ] reading runs
+  - [ ] implement a min heap with following operations
+    - [ ] pop
+    - [ ] push
+  - [ ] step 4
+    - [ ] split the buffer into chunks of size n, and (b-1)n
+    - [ ] create a min heap of size (b-1)n
+    - [ ] populate the heap with (b-1) runs of n elements (each from a different file)
+    - [ ] find a way to mark if a last element from a certain file has been popped
+    - [ ] when a merged buffer is full, write it to file
+    - [ ] pop off the top element until there are no more elements from a certain array
+    - [ ] load another run from that file, and rehapify
+    - [ ] repeat untill all files empty
+    - [ ] the resulting file should get the new smallest filename in tmp dir
+
   - [ ] multiway merge
   - [ ] writing larger runs
   - [ ] repeat untill done
+
+- [ ] counting read, and write operations
 - [ ] testing
 - [ ] report
diff --git a/heap.c b/heap.c
new file mode 100644
index 0000000..587e7ca
--- /dev/null
+++ b/heap.c
@@ -0,0 +1,28 @@
+#include "heap.h"
+#include "status_codes.h"
+
+int heap_push(heap* h, heap_record* in)
+{
+    if (h->length >= h->capacity) {
+        return NO_SPACE;
+    }
+
+    int index = h->length;
+    h->length++;
+    heap_record* last = h->location;
+    last += index;
+    *last = *in;
+
+    if (index == 0) {
+        return SUCCESS;
+    }
+
+    // check if violated heap property
+    heap_record* parent = h->location;
+    parent += ((index - 1) / 2);
+    while (parent->g > last->g) {
+        // just swap them, and check again?
+    }
+    // swim up
+    return SUCCESS;
+}
diff --git a/heap.h b/heap.h
index 00f2bb1..4397dae 100644
--- a/heap.h
+++ b/heap.h
@@ -1,6 +1,7 @@
 #pragma once
 
 #include "record.h"
+#include "stdbool.h"
 
 typedef struct {
     record* location;
@@ -9,9 +10,15 @@ typedef struct {
     bool is_blank;
 } heap_record;
 
-// moves elements to maintain heap property
-int heapify(heap_record* heap);
-// returns the first element, and calls heapify
-int heap_pop(heap_record* heap, heap_record* out);
-// writes to the last elements, and calls heapify
-int heap_pus(heap_record* heap, heap_record* in);
+// almost the same as typedef buffer, but the usage is different, so I think it can be repeated
+typedef struct {
+    heap_record* location;
+    int length;
+    int capacity;
+} heap;
+
+heap new_heap(int size);
+// free_heap is just free(h->location), so it's kinda unnecessary
+
+int heap_pop(heap* h, heap_record* out);
+int heap_push(heap* h, heap_record* in);
diff --git a/makefile b/makefile
index 95df1ee..f72b723 100644
--- a/makefile
+++ b/makefile
@@ -1,7 +1,7 @@
 CFLAGS = -g
 
-build/main: build/main.o build/config.o build/buffer.o
-	clang $(CFLAGS) build/main.o  build/config.o build/buffer.o -o build/main
+build/main: build/main.o build/config.o build/buffer.o build/heap.o
+	clang $(CFLAGS) build/main.o  build/config.o build/buffer.o build/heap.o -o build/main
 
 build/main.o: main.c build
 	clang $(CFLAGS) -c main.c -o build/main.o
@@ -12,6 +12,9 @@ build/config.o: config.c build
 build/buffer.o: buffer.c build
 	clang $(CFLAGS) -c buffer.c -o build/buffer.o
 
+build/heap.o: heap.c build
+	clang $(CFLAGS) -c heap.c -o build/heap.o
+
 build:
 	mkdir -p build
 
diff --git a/status_codes.h b/status_codes.h
index 2a38140..9866402 100644
--- a/status_codes.h
+++ b/status_codes.h
@@ -3,3 +3,4 @@
 #define END_PROGRAM -1
 #define SUCCESS 0
 #define ERROR -2
+#define NO_SPACE -3