#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int main(void) {
  int N;
  cin >> N;
  vector<int> M(N + 1);
  for(int i = 1; i <= N; i++) {
    cin >> M[i];
  }
  vector<int> V(N + 1, 0);
  for(int i = 1; i <= N; i++) {
    if(0 < M[i] - i) {
      V[i] = 1;
    } else if(0 > M[i] - i) {
      V[i] = -1;
    }
  }
  int maxt = 0;
  for(int i = 1; i <= N; i++) {
    maxt = max(maxt, abs(M[i] - i));
  }
  int ans = 0;
  for(int t = 1; t <= maxt; t++) {
    vector<int> NCatStay(30001, 0);
    vector<int> NCatComeFromL(30001, 0);
    vector<int> NCatComeFromR(30001, 0);
    cerr << t << endl;
    for(int i = 1; i <= N; i++) {
      if(0 == V[i]) {
        NCatStay[M[i]]++;
      } else {
        int pos = i + V[i] * t;
        if(V[i] > 0) {
          NCatComeFromL[pos]++;
        } else {
          NCatComeFromR[pos]++;
        }
        if(M[i] == pos) {
          V[i] = 0;
        }
      }
    }
    for(int i = 1; i < 30001; i++) {
      int NCatCome = NCatComeFromL[i] + NCatComeFromR[i];
      ans += NCatStay[i] * NCatCome;
      ans += NCatCome * (NCatCome - 1) / 2;
      if(i > 1) {
        ans += NCatComeFromR[i - 1] * NCatComeFromL[i];
      }
    }
  }
  cout << ans << endl;
  return 0;
}