#include<bits/stdc++.h>
#include<vector>
#include<string>
#include<algorithm>
#include<cmath>
 
#define fast ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define int long long int
#define mod 1000000007
#define inf 1e18+42
#define endl "\n"

#define out1(a) cout<<#a<<" "<<a<<endl
#define out2(a,b) cout<<#a<<" "<<a<<" "<<#b<<" "<<b<<endl
#define out3(a,b,c) cout<<#a<<" "<<a<<" "<<#b<<" "<<b<<" "<<#c<<" "<<c<<endl

#define rep(i,a,b) for(int i=a;i<b;i++)
#define repr(i,a,b) for(int i=a;i>=b;i--)
#define fori(it,A) for(auto it=A.begin();it!=A.end();it++)

#define ft first
#define sd second
#define pb push_back
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define zero(x) memset(x,0,sizeof(x));
 
using namespace std;

int binpow(int,int);
void dfs( vector< vector<int> >&, int , vector<int>& );
void bfs( vector< vector<int> >&, int , vector<int>& );

void solve()
{
    int n;
    cin>>n;

    string s;
    cin>>s;

    int a[3][n];
    zero(a);

    repr(i,s.length()-1,0)
    {
        if ( s[i] == 'R' )
        {
            a[0][s.length()-i-1]++;
        }
        else if ( s[i] == 'G' )
        {
            a[1][s.length()-i-1]++;
        }
        else
        {
            a[2][s.length()-1-i]++;
        }
        rep(j,0,3)
        {
            if ( i != s.length()-1 )
            {
                a[j][s.length()-i-1] += a[j][s.length()-i-2];
            }
        }
    }

    // rep(i,0,n)
    // {
    //     out3(a[0][i],a[1][i],a[2][i]);
    // }
    int ans = 0;
    rep(i,0,s.length())
    {
        rep(j,i+1,s.length()-1)
        {
            if ( s[i] != s[j] )
            {
                char c = 'R' + 'B' + 'G' - s[i] - s[j];
                // out1(c);
                if ( 2*j-i < n )
                {
                    if ( s[2*j-i] == c )
                    {
                        ans--;
                    }
                }
                int k;
                if ( c == 'R' )
                {
                    k = 0;
                }
                else if ( c == 'G' )
                {
                    k = 1;
                }
                else
                {
                    k = 2;
                }
                
                ans += a[k][s.length()-j-2];
            }
        }
    }

    cout<<ans<<endl;
}

signed main()
{
    fast;
    int t = 1;
    // cin>>t;

    while(t--)
    {
        solve();
    }
    return 0;
}

int binpow(int a, int b) {
    int res = 1;
    while (b > 0) {
        if (b & 1)
            res = res * a;
        a = a * a;
        b >>= 1;
    }
    return res;
}

void dfs ( vector< vector<int> > &v , int x , vector<int> &vis )
{
    vis[x] = 1;

    rep(i,0,v[x].size())
    {
        if( vis[v[x][i]] == 0 )
        {
            dfs(v,v[x][i],vis);
        }
    }
}

void bfs( vector< vector<int> > &v , int x , vector<int> &vis )
{
    queue<int> q;
    q.push(x);

    while( !q.empty() )
    {
        int p = q.front();
        q.pop();

        rep(i,0,v[p].size())
        {
            if ( vis[v[p][i]] == 0 )
            {
                vis[v[p][i]] = 1;
                q.push(v[p][i]);
            }
        }
    }
}

Measured memory_bytes: 3700