#include"bits/stdc++.h"
#include <ext/pb_ds/assoc_container.hpp> 
using namespace __gnu_pbds; 
using namespace std;

#define double long double
#define int long long
#define pb push_back 
#define Z(c) (int)(c).size()
#define L(c) c[Z(c)-1]
#define F first
#define S second
#define nl "\n"
#define mii unordered_map<int,int> 
#define all(c) (c).begin(),(c).end()
#define rall(c) (c).rbegin(),(c).rend()
#define rep(i,iv,n) for(int (i)=(iv);(i)<(n);++(i))
#define FO fflush(stdout) 
#define D1(x) cerr <<"At line "<<__LINE__<<" "<<#x<<"="<<x<<nl
#define D2(x,y) cerr <<"At line "<<__LINE__<<" "<<#x<<"="<<x<<" "<<#y<<"="<<y<<nl
#define D3(x,y,z) cerr <<"At line "<<__LINE__<<" "<<#x<<"="<<x<<" "<<#y<<"="<<y<<" "<<#z<<"="<<z<<nl
#define tr(it,ct) for(auto &(it) : (ct))
#define pi acos(-1)
#define prt(ct) for(auto &(it) : (ct)) cerr<<it<<" "; cerr<<nl
#define prtp(ct) for(auto &(it) : (ct)) cerr<<it.F<<" "<<it.S<<nl; cerr<<nl

typedef vector< int > vi;
typedef vector< vi > vvi;
typedef pair< int,int > pii;
typedef pair<pii,pii> ppp;
typedef vector< pii > vp;
typedef tree<int, null_type, less<int>, rb_tree_tag, 
             tree_order_statistics_node_update> baap;

void swap(char &a,char &b)
{ auto tm=a; a=b; b=tm; }

void mina(int &a,int b)
{ a=(a<b?a:b); }

void maxa(int &a,int b)
{ a=(a>b?a:b); }

  const int mod=1000000007;
  const int mod2=998244353;
  const int INF=4e18;
  const int N=2e5+25;
  const int M=1e6;

 void doit()
 { 
   int n; cin>>n; string s; cin>>s; vi v;
   tr(i,s){
     if(i=='R') v.pb(0);
     else if(i=='G') v.pb(1);
     else v.pb(2); 
   }

   vi ct[3]; rep(i,0,3) ct[i].resize(n+1);

   for(int i=n-1;i>=0;--i){
      rep(j,0,3) ct[j][i]=ct[j][i+1];
      ct[v[i]][i]++;
   }

   int ans=0;

   for(int i=0;i<n;++i){
                             
      for(int j=i+1;j<n;++j){
          if(v[j]==v[i]) continue;
        int id;
        if(v[i]+v[j]==1) id=2;
        else if(v[i]+v[j]==2) id=1;
        else id=0;
        ans+=ct[id][j+1];
        if(j+j-i<n&&v[j+j-i]==id) ans--;
      }
   }

   cout<<ans;
                                
 }

signed main()
{ 
   ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

 

   int tc=1;                         
 //  cin>>tc;

  rep(i,1,tc+1)
  { // cout<<"Case #"<<i<<": ";
    
   doit();
   if(i<tc)
   cout<<nl;
  }

 return 0; 
}