#include <iostream>
#include <cstdio>
#include <string>
#include <cstring>
#include <deque>
#include <list>
#include <queue>
#include <stack>
#include <vector>
#include <utility>
#include <algorithm>
#include <map>
#include <set>
#include <complex>
#include <cmath>
#include <limits>
#include <climits>
#include <ctime>
#include <cassert>
#include <numeric>
#include <functional>
#include <bitset>

using namespace std;
using lint = long long int;
long long int INF = 1001001001001001LL;
int inf = 1000000007;
long long int MOD = 1000000007LL;
double PI = 3.1415926535897932;

template<typename T1,typename T2>inline void chmin(T1 &a,const T2 &b){if(a>b) a=b;}
template<typename T1,typename T2>inline void chmax(T1 &a,const T2 &b){if(a<b) a=b;}

#define ALL(a) a.begin(),a.end()
#define RALL(a) a.rbegin(),a.rend()

/* do your best */

// quoted from beet-aizu
template <typename T, typename E, typename F, typename G>
struct SegmentTree{
    // using F = function<T(T, T)>
    // using G = function<T(T, E)>
    int n;
    F f;
    G g;
    T ti;
    vector<T> dat;
    SegmentTree(){};
    SegmentTree(F f,G g,T ti):f(f),g(g),ti(ti){}
    void init(int n_){    
        n=1;
        while(n<n_) n<<=1;
        dat.assign(n<<1,ti);
    }
    void build(const vector<T> &v){
        int n_=v.size();
        init(n_);
        for(int i=0;i<n_;i++) dat[n+i]=v[i];
        for(int i=n-1;i;i--)
            dat[i]=f(dat[(i<<1)|0],dat[(i<<1)|1]);
    }
    void update(int k,const E &x){
        k += n;
        dat[k] = g(dat[k], x);
        while(k>>=1)
            dat[k]=f(dat[(k<<1)|0],dat[(k<<1)|1]);    
    }
    T operator [](int k) const { return dat[k+n]; }
    T query(int a,int b) const {
        T vl=ti,vr=ti;
        for(int l=a+n,r=b+n;l<r;l>>=1,r>>=1) {
            if(l&1) vl=f(vl,dat[l++]);
            if(r&1) vr=f(dat[--r],vr);
        }
        return f(vl,vr);
    }

    /* TODO わからない 聞く 
    template<typename C>
    int find(int a,int b,C &check,int k,int l,int r){
        if(!check(dat[k])||r<=a||b<=l) return -1;
        if(k>=n) return k-n;
        int m=(l+r)>>1;
        int vl=find(a,b,check,(k<<1)|0,l,m);
        if(~vl) return vl;
        return find(a,b,check,(k<<1)|1,m,r);
    }
    template<typename C>
    int find(int a,int b,C &check){
        return find(a,b,check,1,0,n);
    }*/
    
};

int main(){
  using T = lint;  // type T
  using E = lint;  // type E
  auto f = [](T a, T b){ // return type T value
    return a + b;
  };
  auto gg = [](T a, E b){ // return type T value
    return b;  // return b;
  };
  T ti = 0;  // identity element
  SegmentTree<T, E, decltype(f), decltype(gg)> sr(f, gg, ti);  // don't change
  SegmentTree<T, E, decltype(f), decltype(gg)> sg(f, gg, ti);  // don't change
  SegmentTree<T, E, decltype(f), decltype(gg)> sb(f, gg, ti);  // don't change

  int n; cin >> n;
  string s; cin >> s;
  vector<lint> r(n);
  vector<lint> g(n);
  vector<lint> b(n);

  for (int i = 0; i < n; i++) {
    if (s[i] == 'R') r[i] = 1;
    if (s[i] == 'G') g[i] = 1;
    if (s[i] == 'B') b[i] = 1;
  }

  sr.build(r);
  sg.build(g);
  sb.build(b);

  lint ans = 0;
  for (int i = 0; i < n; i++) {
    for (int k = i + 1; k < n; k++) {
      
      if (s[i] == s[k]) continue;
      char need;
      if (s[i] != 'R' and s[k] != 'R') need = 'R';
      if (s[i] != 'G' and s[k] != 'G') need = 'G';
      if (s[i] != 'B' and s[k] != 'B') need = 'B';
      
      if ((k - i) % 2 == 0) {
        int j = (k - i) / 2 + i;

        if (need == 'R') ans += sr.query(i, j) + sr.query(j + 1, k + 1);
        if (need == 'G') ans += sg.query(i, j) + sg.query(j + 1, k + 1);
        if (need == 'B') ans += sb.query(i, j) + sb.query(j + 1, k + 1);

      } else {

        if (need == 'R') ans += sr.query(i, k);
        if (need == 'G') ans += sg.query(i, k);
        if (need == 'B') ans += sb.query(i, k);
      }

      // cout << i << " " << k << " " << ans << ", need = " << need << endl;
    }
  }
  
  cout << ans << endl;
}


Measured memory_bytes: 3344