void main() {
	const N = readInt;
	auto A = new int[N];
	foreach (i; 0 .. N) {
		A[i] = readInt;
	}
	int ans;
	ans += A[0] - 1;
	foreach (i; 1 .. N) {
		ans += A[i] - A[i - 1] - 1;
	}
	writeln(ans);
}

import std,core.bitop;
string[]_R;
string readString(){while(_R.empty){_R=readln.chomp.split;}auto ret=_R.front;_R.popFront;return ret;}
int readInt(){return readString.to!int;}
long readLong(){return readString.to!long;}
real readReal(){return readString.to!real;}
bool chmin(T)(ref T A,T B){if(A>B){A=B;return true;}else{return false;}}
bool chmax(T)(ref T A,T B){if(A<B){A=B;return true;}else{return false;}}
int lowerBound(T)(T[]A,T x){int L=-1,R=cast(int)A.length;while(R-L>1){int mid=(L+R)/2;(A[mid]<x?L:R)=mid;}return R;}
int upperBound(T)(T[]A,T x){int L=-1,R=cast(int)A.length;while(R-L>1){int mid=(L+R)/2;(A[mid]<=x?L:R)=mid;}return R;}