package main

import . "fmt"
import . "os"
import bf "bufio"

func main() {
	rd := bf.NewReader(Stdin)
	var n int
	Fscan(rd,&n)
	a := make([]int, n)
	for i := range a {
		Fscan(rd,&a[i])
	}
	Println(a[n-1]-n)
}