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


// a new data structure defined. Please refer below
// GNU link : https://goo.gl/WVDL6g
typedef tree<int, null_type, less_equal<int>, rb_tree_tag,
             tree_order_statistics_node_update>
    ordered_set;


#define pf                  printf
#define sf(a)               scanf("%d",&a)
#define sfl(a)              scanf("%lld",&a)
#define sff(a,b)            scanf("%d %d",&a,&b)
#define sffl(a,b)           scanf("%lld %lld",&a,&b)
#define sfff(a,b,c)         scanf("%d %d %d",&a,&b,&c)
#define sfffl(a,b,c)        scanf("%lld %lld %lld",&a,&b,&c)
#define sffff(a,b,c,d)      scanf("%d %d %d %d",&a,&b,&c,&d)
#define sffffl(a,b,c,d)     scanf("%lld %lld %lld %lld",&a,&b,&c,&d)
#define sfffff(a,b,c,d,e)   scanf("%d %d %d %d %d",&a,&b,&c,&d,&e)
#define sfffffl(a,b,c,d,e)  scanf("%lld %lld %lld %lld %lld",&a,&b,&c,&d,&e)
#define sfc(a)              scanf("%c",&a)
#define pii                 pair<int,int>
#define ms(a,b)             memset(a,b,sizeof(a))
#define pb(a)               push_back(a)
#define pbp(a,b)            push_back({a,b})
#define db                  double
#define ft                  float
#define ll                  long long
#define ull                 unsigned long long
#define pii                 pair<int,int>
#define ff                  first
#define ss                  second
#define sz(x)               x.size()
#define all(x)              x.begin(),x.end()
#define CIN                 ios_base::sync_with_stdio(0); cin.tie(0)
#define max3(a, b, c)       max(a, b) > max(b, c) ? max(a, b) : max(b, c)
#define min3(a, b, c)       min(a, b) < min(b, c) ? min(a, b) : min(b, c)
#define for0(i,n)           for(int i=0;i<n;i++)
#define for1(i,n)           for(int i=1;i<=n;i++)
#define forrev(i,n)         for(int i=n-1; i>=0; i--)
#define forab(i,a,b)        for(int i=a;i<=b;i++)
#define forba(i,b,a)        for(int i=b;i>=a;i--)
#define stlloop(x)          for(__typeof(x.begin()) it=x.begin();it!=x.end();it++)
#define gcd(a, b)           __gcd(a, b)
#define lcm(a, b)           ((a)*((b)/gcd(a,b)))
#define case1(z)            cout<<"Case "<<z<<": "
#define case2(z)            printf("Case %d: ",z)
#define PI                  acos(-1) //3.14159265358979323846264338328
#define valid(tx,ty)        tx>=0 && tx<row && ty>=0 && ty<col
#define intlim              2147483648
#define N                   40005
#define inf                 100000008
#define mod                 1000000007

/*------------------------------Graph Moves----------------------------*/
//const int fx[]={+1,-1,+0,+0};
//const int fy[]={+0,+0,+1,-1};
//const int fx[]={+0,+0,+1,-1,-1,+1,-1,+1};   // Kings Move
//const int fy[]={-1,+1,+0,+0,+1,+1,-1,-1};  // Kings Move
//const int fx[]={-2, -2, -1, -1,  1,  1,  2,  2};  // Knights Move
//const int fy[]={-1,  1, -2,  2, -2,  2, -1,  1}; // Knights Move
/*---------------------------------------------------------------------*/



ll a[N],b[N],c[N];


int main()
{
    ios_base :: sync_with_stdio(0); cin.tie(0); cout.tie(0);
    ll n,i,j,k,x,y=0,l,ans=0;
    cin>>n;
    string g;
    cin>>g;
    l=g.length();
    for(i=l-1;i>=0;i--)
    {
        if(g[i]=='R') a[i]=a[i+1]+1;
        else a[i]=a[i+1];
        if(g[i]=='G') b[i]=b[i+1]+1;
        else b[i]=b[i+1];
        if(g[i]=='B') c[i]=c[i+1]+1;
        else c[i]=c[i+1];
    }
    /*for(i=0;i<l;i++)
        cout<<a[i]<<" ";
    cout<<endl;
    for(i=0;i<l;i++)
        cout<<b[i]<<" ";
    cout<<endl;
    for(i=0;i<l;i++)
        cout<<c[i]<<" ";
    cout<<endl;*/
    for(i=0;i<l-2;i++)
    {
        for(j=i+1;j<l-1;j++)
        {
            x=j-i;
            x=j+x;
            if(g[i]!=g[j])
            {
                //cout<<i<<" "<<j<<" "<<x<<endl;
                if(g[i]=='R' && g[j]=='G')
                {
                    y=c[j+1];
                    if(g[x]=='B')
                        y-=1;
                }
                else if(g[i]=='G' && g[j]=='R')
                {
                    y=c[j+1];
                    if(g[x]=='B')
                        y-=1;
                }
                else if(g[i]=='G' && g[j]=='B')
                {
                    y=a[j+1];
                    if(g[x]=='R')
                        y-=1;
                }
                else if(g[i]=='B' && g[j]=='G')
                {
                    y=a[j+1];
                    if(g[x]=='R')
                        y-=1;
                }
                else if(g[i]=='R' && g[j]=='B')
                {
                    y=b[j+1];
                    if(g[x]=='G')
                        y-=1;
                }
                else if(g[i]=='B' && g[j]=='R')
                {
                    y=b[j+1];
                    if(g[x]=='G')
                        y-=1;
                }
                ans+=y;
            }
            //cout<<y<<endl;
        }
    }
    cout<<ans<<endl;
	return 0;
}


























Measured memory_bytes: 3680