diff --git a/main.go b/main.go
index c9c9fcb..9309b3d 100644
--- a/main.go
+++ b/main.go
@@ -4,12 +4,31 @@ import (
 	"container/heap"
 	"fmt"
 	"math/rand"
+	"os"
 	"sort"
+	"strconv"
 	"time"
 )
 
+const usage = "smerge [count, count, ... count]"
+
 func main() {
-	for i := range merge(source(500), source(100), source(200)) {
+	args := os.Args[1:]
+	if len(args) < 1 {
+		fmt.Fprintf(os.Stderr, "usage: %v\n", usage)
+		os.Exit(1)
+	}
+	srcs := []<-chan int{}
+	for _, arg := range args {
+		i, err := strconv.Atoi(arg)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "%v\n", err)
+			os.Exit(1)
+		}
+
+		srcs = append(srcs, source(i))
+	}
+	for i := range merge(srcs...) {
 		fmt.Printf("%20d\n", i)
 	}
 }