#include <iostream>
#include <vector>
#include <map>
using namespace std;
int N;
struct X{
	float no;
	int goal;
};

void CheckMeet(vector<X> &cat,int &ans)
{
	map<float,int> myMap;
	map<float,int>::iterator mit;
	float i;
	for (i=0;i<N;i++){
		mit=myMap.find(cat[i].no);
		if (mit!=myMap.end()){
			(*mit).second++;
		}else{
			myMap[cat[i].no]=1;
		}
	}
	for (mit=myMap.begin();mit!=myMap.end();mit++){
		int n=(*mit).second;
		if (n>1){
			ans+=n*(n-1)/2;
		}
	}
	myMap.clear();
}
int main(int argc, char* argv[])
{
	float i;
	cin>>N;
	vector<X> cat(N);
	int diffNum=0;
	for (i=0;i<N;i++){
		cat[i].no=i+1;
		cin>>cat[i].goal;
		if (cat[i].no!=cat[i].goal){
			diffNum++;
		}
	}
	int ans=0;
	while (diffNum>0){
		for (i=0;i<N;i++){
			if (cat[i].no>cat[i].goal){
				cat[i].no-=0.5;
			}else if (cat[i].no<cat[i].goal){
				cat[i].no+=0.5;
			}else{
				continue;
			}
			if (cat[i].no==cat[i].goal){
				diffNum--;
			}
		}
		CheckMeet(cat,ans);
	}
	cout<<ans<<endl;
	return 0;
}