#include <iostream>
#include <string>
#include <algorithm>
#include <functional>
#include <vector>
#include <stack>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <cstdio>
#include <cmath>
#include <tuple>
#include <iomanip>
#include <numeric>
#include <unordered_map>
#include <sstream>   
#include<limits.h>
#include<float.h>
#include<list>
#include <array>
#include <complex>
#include<stdio.h>
#include<string.h>
#include <bitset>

using namespace std;
#define int  long long
 
#define I32_MAX 2147483647
#define I64_MAX 9223372036854775807LL
#define I64_MAX2 1223372036854775807LL
#define INF I64_MAX2
#define MOD 1000000007
#define MEM_SIZE 10000
#define DEBUG_OUT true
#define ALL(x) (x).begin(),(x).end()

// int DP[MEM_SIZE][MEM_SIZE] = {0};
// int GMEM[MEM_SIZE][MEM_SIZE] = {0};
template<typename T> void DEBUG(T e){if(DEBUG_OUT == false)return; std::cout << e <<" ";}
template<typename T> void DEBUG(const std::vector<T>& v){if(DEBUG_OUT == false)return;for(const auto& e : v){std::cout<< e << " "; } std::cout << std::endl;}
template<typename T> void DEBUG(const std::vector<std::vector<T> >& vv){if(DEBUG_OUT == false)return;for(const auto& v : vv){ DEBUG(v); } }
template<class T,class... Ts> void DEBUG(T d, Ts... e){if(DEBUG_OUT == false)return;DEBUG(d);DEBUG(e...);}
template <class T> void corner(bool flg, T hoge) {if (flg) {cout << hoge << endl; exit(0);}}
template< typename T1, typename T2 > inline bool chmax(T1 &a, T2 b) { return a < b && (a = b, true); }
template< typename T1, typename T2 > inline bool chmin(T1 &a, T2 b) { return a > b && (a = b, true); }


void solve(void)
{
  int N;
  cin>>N;
  vector<int> R,G,B;
  for (int i = 0; i < N; i++)
  {
    char X; cin>>X;
    if(X == 'R') R.push_back(i+1);
    if(X == 'G') G.push_back(i+1);
    if(X == 'B') B.push_back(i+1);
  }
  int ANS = R.size()*G.size()*B.size();
  for (int i = 0; i < R.size(); i++)
  {
    for (int j = 0; j < G.size(); j++)
    {
      int xR = R[i];
      int xG = G[j];
      if((find(ALL(B),(xR+xG)/2) != B.end())&&(xR+xG)%2 == 0)
      {
        ANS--;
      }
      if((find(ALL(B),max(xR,xG) + abs(xR - xG)) != B.end()))ANS--;
      if((find(ALL(B),min(xR,xG) - abs(xR - xG)) != B.end()))ANS--;
    }
    
  }
  cout<<ANS<<endl;
  
  
  return;
}

int32_t main(int32_t argc, const char *argv[])
{
  std::ios::sync_with_stdio(false);
  std::cin.tie(0);

  std::cout << std::fixed;
  std::cout << std::setprecision(9);
  solve();

  return 0;
}
