package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"
)

func main() {
//  file, _ := os.Open("test")
  file, _ := os.Open("input")
  defer file.Close()
  scanner := bufio.NewScanner(file)
  diskMap := []string{}
  for scanner.Scan() {
    line := scanner.Text()
    diskMap = append(diskMap, strings.Split(line, "")...)
  }
  fileID := 0
  blockSize := 0
  freeSpace := 0
  blocks := []string{}
  for i := range diskMap {
    if i % 2 == 0 {
      blockSize, _ = strconv.Atoi(diskMap[i])
      for j:=0;j<blockSize;j++ {
        blocks = append(blocks, strconv.Itoa(fileID))
      }
      fileID++
    } else {
      freeSpace, _ = strconv.Atoi(diskMap[i])
      for j:=0;j<freeSpace;j++ {
        blocks = append(blocks, ".")
      }
    }
  }
  for i := range blocks {
    if blocks[i] == "." {
      for j:=len(blocks)-1;j>i;j-- {
        if blocks[j] != "." {
          blocks[i] = blocks[j]
          blocks[j] = "."
          break
        }
      }
    }
  }
  checksum := 0
  for i := range blocks {
    blockID, _ := strconv.Atoi(blocks[i])
    checksum = checksum + i * blockID
  }
  fmt.Println(checksum)
}