#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
//#include <boost/multiprecision/cpp_ll.hpp>
//typedef boost::multiprecision::cpp_ll ll;
typedef long double dd;
#define i_7 (ll)(1E9+7)
//#define i_7 998244353
#define i_5 i_7-2
ll mod(ll a){
    ll c=a%i_7;
    if(c>=0)return c;
    return c+i_7;
}
typedef pair<ll,ll> l_l;
ll inf=(ll)1E16;
#define rep(i,l,r) for(ll i=l;i<=r;i++)
#define pb push_back
ll max(ll a,ll b){if(a<b)return b;else return a;}
ll min(ll a,ll b){if(a>b)return b;else return a;}
void Max(ll &pos,ll val){pos=max(pos,val);}//Max(dp[n],dp[n-1]);
void Min(ll &pos,ll val){pos=min(pos,val);}
void Add(ll &pos,ll val){pos=mod(pos+val);}
dd EPS=1E-9;
#define endl "\n"
#define fastio ios::sync_with_stdio(false); cin.tie(0); cout.tie(0);



int main(){fastio
    ll n;cin>>n;
    string s;cin>>s;
    ll r=0,g=0,b=0;
    rep(i,0,n-1){
        if(s[i]=='R'){
            r++;
        }else if(s[i]=='G'){
            g++;
        }else{
            b++;
        }
    }
    ll ans=r*g*b;
    rep(i,1,n){
        rep(j,0,n-1){
            if(j+2*i>=n){
                break;
            }
            if(s[j]!=s[j+i] && s[j+i]!=s[j+2*i] && s[j+2*i]!=s[j]){
                ans--;
            }
        }
    }
    cout<<ans<<endl;
    
    return 0;
}



