/*
 * Author: Anmol Choudhary
 */
// #include <ext/pb_ds/assoc_container.hpp>
// #include <ext/pb_ds/tree_policy.hpp>
#include<bits/stdc++.h>
// using namespace __gnu_pbds;
using namespace std;
#define ll long long
#define pb push_back
#define vi vector<int>
#define rep0(a,b) for(int a=0;a<b;a++)
#define rep1(a,b) for(int a=1;a<=b;a++)
#define repp(a,b,c) for(int a=b;a<c;a++)
#define in insert
#define len length()
#define si size()
#define lb lower_bound
#define ub upper_bound
#define beg begin()
#define en end()
#define f first
#define s second
#define pr(a) cout<<a
#define pr2(a,b) cout<<a<<" "<<b<<"\n"
#define nx cout<<"\n"
#define int long long
//void __print(int x) {cerr << x;}
void __print(long x) {cerr << x;}
void __print(long long x) {cerr << x;}
void __print(unsigned x) {cerr << x;}
void __print(unsigned long x) {cerr << x;}
void __print(unsigned long long x) {cerr << x;}
void __print(float x) {cerr << x;}
void __print(double x) {cerr << x;}
void __print(long double x) {cerr << x;}
void __print(char x) {cerr << '\'' << x << '\'';}
void __print(const char *x) {cerr << '\"' << x << '\"';}
void __print(const string &x) {cerr << '\"' << x << '\"';}
void __print(bool x) {cerr << (x ? "true" : "false");}
                                                     
template<typename T, typename V>
void __print(const pair<T, V> &x) {cerr << '{'; __print(x.first); cerr << ','; __print(x.second); cerr << '}';}
template<typename T>
void __print(const T &x) {int f = 0; cerr << '{'; for (auto &i: x) cerr << (f++ ? "," : ""), __print(i); cerr << "}";}
void _print() {cerr << "]"<<endl;}
template <typename T, typename... V>
void _print(T t, V... v) {__print(t); if (sizeof...(v)) cerr << ", "; _print(v...);}
#ifndef ONLINE_JUDGE
#define deb(x...) cerr << "[" << #x << "] = ["; _print(x)
#else
#define deb(x...)
#endif
const ll mod = 1000000007;
const ll maxn = 500005;
const ll mm = 1e+18;
void solve()
{
    int n;
    cin>>n;
    vector<int>v[3];
    string s;
    cin>>s;
    rep0(i,n){
        if(s[i]=='R') v[0].pb(i);
        if(s[i]=='B') v[1].pb(i);
        if(s[i]=='G') v[2].pb(i);
    }
    int f1=v[0].si;
    int f2=v[1].si;
    int f3=v[2].si;
    int an=f1*f2*f3;
    rep0(i,n)rep0(j,n){
        int x=i;
        int y=x+1+j;
        int z=y+1+j;
        if(z>=n) break;
        if(s[x]!=s[y]&&s[x]!=s[z]&&s[y]!=s[z]) an--;
    }
    pr(an);
}
signed main()
{
    ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    int t=1;
    //cin>>t;
    while(t--){
        solve();
        //nx;
    }
    return 0;
}
