diff --git a/11/day11.c b/11/day11.c
index a64718b..f492edb 100644
--- a/11/day11.c
+++ b/11/day11.c
@@ -24,7 +24,7 @@ int initialFieldValue(int x, int y) {
     // manually set a nullbyte after the hundreds digit
     itoa[len-2] = 0;
     int parsed = (int) strtol(&itoa[len-3], NULL, 10);
-    return parsed;
+    return parsed - 5;
 }
 
 void setFields(int fields[DIMENSIONS][DIMENSIONS]) {
diff --git a/11/day11_2.c b/11/day11_2.c
new file mode 100644
index 0000000..5ee0342
--- /dev/null
+++ b/11/day11_2.c
@@ -0,0 +1,86 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+#define SERIAL 7347
+#define DIMENSIONS 300
+
+int initialFieldValue(int x, int y) {
+    int id = x + 10;
+    int power = id * y + SERIAL;
+    power *= id;
+    char itoa [10];
+    int len = sprintf(itoa, "%d", power);
+    if (len < 3) {
+        return 0;
+    }
+    // manually set a nullbyte after the hundreds digit
+    itoa[len-2] = 0;
+    int parsed = (int) strtol(&itoa[len-3], NULL, 10);
+    return parsed - 5;
+}
+
+void setFields(int fields[DIMENSIONS][DIMENSIONS]) {
+    for (int i=0; i<DIMENSIONS; i++) {
+        for (int j=0; j<DIMENSIONS; j++) {
+            fields[i][j] = initialFieldValue(i+1, j+1);
+        }
+    }
+}
+
+// https://en.wikipedia.org/wiki/Summed-area_table
+void setSummedArea(int sums[DIMENSIONS][DIMENSIONS], int input[DIMENSIONS][DIMENSIONS]) {
+    sums[0][0] = input[0][0];
+    // Topmost row
+    for (int x=1; x<DIMENSIONS; x++) {
+        int y = 0;
+        sums[x][y] = input[x][y] + sums[x-1][y];
+    }
+
+    // Leftmost column
+    for (int y=1; y<DIMENSIONS; y++) {
+        int x = 0;
+        sums[x][y] = input[x][y] + sums[x][y-1];
+    }
+
+    for (int x=1; x<DIMENSIONS; x++) {
+        for (int y=1; y<DIMENSIONS; y++) {
+            sums[x][y] = input[x][y] + sums[x][y-1] + sums[x-1][y] - sums[x-1][y-1];
+        }
+    }
+}
+
+int max(int a, int b) {
+    return a > b ? a : b;
+}
+
+int calculateNeighborhood(int fields[DIMENSIONS][DIMENSIONS], int x, int y, int size) {
+    return fields[x-1][y-1] + fields[x+size][y+size] - fields[x-1][y+size] - fields[x+size][y-1];
+}
+
+int main() {
+    int fields[DIMENSIONS][DIMENSIONS];
+    setFields(fields);
+    int summedAreaFields[DIMENSIONS][DIMENSIONS];
+    setSummedArea(summedAreaFields, fields);
+    
+    // Part 1
+    int maxPower = -999999999;
+    int maxX, maxY;
+    int maxSize = 0;
+    for (int x=1; x<DIMENSIONS-3; x++) {
+        for (int y=1; y<DIMENSIONS-3; y++) {
+            for (int size=3; size<DIMENSIONS-max(x, y); size++) {
+                int moore = calculateNeighborhood(summedAreaFields, x, y, size);
+                if (moore > maxPower) {
+                    maxPower = moore;
+                    maxX = x + 1;
+                    maxY = y + 1;
+                    maxSize = size + 1;
+                }
+            }
+        }
+    }
+    printf("x: %d, y: %d, size: %d, power: %d\n", maxX, maxY, maxSize, maxPower);
+
+    return 0;
+}
diff --git a/README.md b/README.md
index 78250b1..8ede50f 100644
--- a/README.md
+++ b/README.md
@@ -4,7 +4,7 @@
 ## Tickets
 | Lang.  | 1 | 2 | 3 | 4 | 5 |
 |:-------|---|---|---|---|---|
-| C      | x | x | x |   |   |
+| C      | x | x | x | x |   |
 | Go     | x | x |   |   |   |
 | Kotlin | x | x |   |   |   |
 | Python | x |   |   |   |   |