//R<3S
#include <bits/stdc++.h>
#define DECIMAL(n)  std::cout << std::fixed;std::cout << std::setprecision(n);
#define FAST std::ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define hell 1000000007
#define PI 3.14159265358979323844
#define mp make_pair
#define pb push_back
#define fi first 
#define se second
#define ALL(v) v.begin(), v.end()
#define SORT(v) sort(ALL(v))  
#define REVERSE(v) reverse(ALL(v))
#define endl "\n"
#define vecmax(v) max_element(all(v))
#define vecmin(v) min_element(all(v))
#define GCD(m,n) __gcd(m,n)
#define LCM(m,n) m*(n/GCD(m,n))
#define inputarr(a,n) for(int i=0;i<n;++i) cin>>a[i]
#define initarr(a,n,x) for (int i=0;i<n;++i) a[i]=x
#define rep(i, n)    for(int i = 0; i < (n); ++i)
#define repA(i, a, n)  for(int i = a; i <= (n); ++i)
#define repD(i, a, n)  for(int i = a; i >= (n); --i)
#define trav(x) for(auto i : x)
#define sz(a) (int)a.size()
#define sl(a) (int)a.length()
#define invect(data,n) for(int i = 0;i<n;i++){int tmp;cin>>tmp;data.pb(tmp);}
#define inset(data,n) for(int i = 0;i<n;i++){int tmp;cin>>tmp;data.insert(tmp);}
#define ll long long
#define int unsigned long long
#define ld long double 
#define pii std::pair<int, int> 
#define pll std::pair<ll, ll>  
#define vi vector<int>  
#define vl vector<ll>
#define vvi vector<vi > 
#define vii vector<pii >
#define mii map<int,int>
#define mll map<ll,ll>
#define trace1(x)                cerr<<#x<<": "<<x<<endl
#define trace2(x, y)             cerr<<#x<<": "<<x<<" | "<<#y<<": "<<y<<endl
#define trace3(x, y, z)          cerr<<#x<<":" <<x<<" | "<<#y<<": "<<y<<" | "<<#z<<": "<<z<<endl
#define trace4(a, b, c, d)       cerr<<#a<<": "<<a<<" | "<<#b<<": "<<b<<" | "<<#c<<": "<<c<<" | "<<#d<<": "<<d<<endl
#define trace5(a, b, c, d, e)    cerr<<#a<<": "<<a<<" | "<<#b<<": "<<b<<" | "<<#c<<": "<<c<<" | "<<#d<<": "<<d<<" | "<<#e<< ": "<<e<<endl
#define trace6(a, b, c, d, e, f) cerr<<#a<<": "<<a<<" | "<<#b<<": "<<b<<" | "<<#c<<": "<<c<<" | "<<#d<<": "<<d<<" | "<<#e<< ": "<<e<<" | "<<#f<<": "<<f<<endl


using namespace std;

void solve()
  {
    int n;
    cin>>n;
    string s;
    int r[2*n]={0},g[2*n]={0},b[2*n]={0};
    cin>>s;
    if(s[0]=='R')r[0]=1;
    else if(s[0]=='G')g[0]=1;
    else if(s[0]=='B')b[0]=1;
    repA(i,1,2*n)
    {
        if(i<n){
        if(s[i]=='R'){r[i]=r[i-1]+1;g[i]=g[i-1];b[i]=b[i-1];}
        else if(s[i]=='G'){r[i]=r[i-1];g[i]=g[i-1]+1;b[i]=b[i-1];}
        else if(s[i]=='B'){r[i]=r[i-1];g[i]=g[i-1];b[i]=b[i-1]+1;}}
        else{g[i]=g[i-1];r[i]=r[i-1];b[i]=b[i-1];}

    }
    int forbidden,sum=0;
    repA(i,0,n-3)
    {
        char first=s[i];
        repA(j,i+1,n-2)
        {
            if(s[j]!=s[i])
            {
                char first=s[i];
                char second=s[j];
                if(first=='R'&&second=='G'){forbidden=j+j-i;sum+=b[n-1]-b[j];sum-=b[forbidden]-b[forbidden-1];}
                else if(first=='R'&&second=='B'){forbidden=j+j-i;sum+=g[n-1]-g[j];sum-=g[forbidden]-g[forbidden-1];}
                else if(first=='G'&&second=='R'){forbidden=j+j-i;sum+=b[n-1]-b[j];sum-=b[forbidden]-b[forbidden-1];}
                else if(first=='G'&&second=='B'){forbidden=j+j-i;sum+=r[n-1]-r[j];sum-=r[forbidden]-r[forbidden-1];}
                else if(first=='B'&&second=='R'){forbidden=j+j-i;sum+=g[n-1]-g[j];sum-=g[forbidden]-g[forbidden-1];}
                else if(first=='B'&&second=='G'){forbidden=j+j-i;sum+=r[n-1]-r[j];sum-=r[forbidden]-r[forbidden-1];}

            }
        }
    }
    cout<<sum<<endl;

  }



signed main()
{
   FAST

   int t;
   t=1;
   //cin>>t;
   while(t--)
    {
        solve();
    }


   return 0;
}


Measured memory_bytes: 3780