diff --git a/MissingInteger.go b/MissingInteger.go
new file mode 100644
index 0000000..5287e68
--- /dev/null
+++ b/MissingInteger.go
@@ -0,0 +1,29 @@
+package codility
+
+// https://codility.com/programmers/task/missing_integer/
+func MissingInteger(A []int) int {
+	positiveMin := 0
+	for _, e := range A {
+		if e > 0 && (positiveMin == 0 || e < positiveMin) {
+			positiveMin = e
+		}
+	}
+	if positiveMin == 0 || positiveMin > 1 {
+		return 1
+	}
+
+	n := len(A)
+	possibleMissings := make([]bool, n-1)
+	for _, e := range A {
+		minOffset := e - positiveMin - 1
+		if minOffset >= 0 && minOffset < len(possibleMissings) {
+			possibleMissings[minOffset] = true
+		}
+	}
+	for i, e := range possibleMissings {
+		if !e {
+			return positiveMin + i + 1
+		}
+	}
+	return positiveMin + n
+}