#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx,avx2,fma")

#include<bits/stdc++.h>
#include<ext/pb_ds/tree_policy.hpp>
#include<ext/pb_ds/assoc_container.hpp>
using namespace std;
using namespace __gnu_pbds;
#define ll long long
#define inf 2000000000
#define infLL 2000000000000000000
#define MAX 1000006
#define sf(a) scanf("%d", &a)
#define sfl(a) scanf("%lld", &a)
#define pf(a) printf("%d\n", a)
#define pfl(a) printf("%lld\n", a)
#define Case(t) printf("Case %d: ", t)
#define pii pair<int, int>
#define MOD 1000000007
#define mod 998244353
#define PI acos(-1.0)
#define eps 1e-9
#define mem(a, b) memset(a, b, sizeof(a))
#define FASTIO ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0);

#define error(args...) { string _s = #args; replace(_s.begin(), _s.end(), ',', ' '); stringstream _ss(_s); istream_iterator<string> _it(_ss); err(_it, args); }

inline int Set(int N, int pos){return N=N | (1<<pos);}
inline int Reset(int N, int pos){return N=N & ~(1<<pos);}
inline bool Check(ll N, ll pos){return (bool)(N & (1LL<<pos));}

inline void normal(ll &a) { a %= mod; (a < 0) && (a += mod); }
inline ll modMul(ll a, ll b) { a %= mod, b %= mod; normal(a), normal(b); return (a * b) % mod; }
inline ll modAdd(ll a, ll b) { a %= mod, b %= mod; normal(a), normal(b); return (a + b) % mod; }
inline ll modSub(ll a, ll b) { a %= mod, b %= mod; normal(a), normal(b); a -= b; normal(a); return a; }
inline ll modPow(ll b, ll p) { ll r = 1; while (p) { if (p & 1LL) r = modMul(r, b); b = modMul(b, b); p >>= 1LL; } return r; }
inline ll modInverse(ll a) { return modPow(a, mod - 2); }
inline ll modDiv(ll a, ll b) { return modMul(a, modInverse(b)); }

ll fast_exp(ll x, ll n, ll m)
{
    ll res = 1;
    while(n>0)
    {
        if(n%2==1)
            res = (res * x) % m;
        x = (x * x) % m;
        n/=2;
    }
    return res%m;
}

void err(istream_iterator<string> it) {}
template<typename T, typename... Args>
void err(istream_iterator<string> it, T a, Args... args)
{
    cerr << *it << " = " << a << endl;
    err(++it, args...);
}

clock_t t_Start;
void Start()
{
    t_Start = clock();
}
void End()
{
    double Time = (double)(clock()-t_Start)/CLOCKS_PER_SEC;
    error(Time);
}

typedef tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update>orderedSet;
typedef tree<int,null_type,greater<int>,rb_tree_tag,tree_order_statistics_node_update>orderedSet1;

int main()
{
    //freopen("in.txt","r",stdin);
    //freopen("out.txt","w",stdout);
    //Start();

    FASTIO;
    int n;
    string s;
    cin>>n>>s;
    int R[n+5], G[n+5], B[n+5];
    mem(R, 0);
    mem(G, 0);
    mem(B, 0);
    for(int i = n-1; i >= 0; i--)
    {
        if(s[i]=='R')
            R[i]+=(R[i+1]+1);
        else
            R[i] = R[i+1];
    }
    for(int i = n-1; i >= 0; i--)
    {
        if(s[i]=='G')
            G[i]+=(G[i+1]+1);
        else
            G[i] = G[i+1];
    }
    for(int i = n-1; i >= 0; i--)
    {
        if(s[i]=='B')
            B[i]+=(B[i+1]+1);
        else
            B[i] = B[i+1];
    }
    ll ans = 0;
    for(int i = 0; i < n; i++)
    {
        for(int j = i + 1; j < n; j++)
        {
            if(s[i]!=s[j])
            {
                int pos = (2 * j) - i;
                if(s[i]!='R' && s[j]!='R')
                {
                    ans+=R[j+1];
                    if(s[pos]=='R')
                    {
                        ans--;
                        ///error(i, j, pos);
                    }
                }
                else if(s[i]!='G' && s[j]!='G')
                {
                    ans+=G[j+1];
                    if(s[pos]=='G')
                    {
                        ans--;
                        ///error(i, j, pos);
                    }
                }
                else if(s[i]!='B' && s[j]!='B')
                {
                    ans+=B[j+1];
                    if(s[pos]=='B')
                    {
                        ans--;
                        ///error(i, j, pos);
                    }
                }
            }
        }
    }
    cout<<ans<<endl;

    //End();
    return 0;
}


Measured memory_bytes: 3720