        #include <bits/stdc++.h>
        using namespace std;
        long long n,ans,pref[4001][3],vals[4001];
        string s;
         
        int main(){
            cin >> n >> s;
            for(int i = 0 ; i < n ; i += 1){
                if(s[i] == 'R'){
                    vals[i] = 0;
                }else if(s[i] == 'G'){
                    vals[i] = 1;
                }else{
                    vals[i] = 2;
                }
            }
            for(int i = n-1 ; i >= 0 ; i -= 1){
                for(int j = 0 ; j < 3 ; j += 1){
                    pref[i][j] = pref[i+1][j];
                }
                pref[i][vals[i]] += 1;
            }
            for(int i = 0 ; i+1 < n ; i += 1){
                for(int j = i+1 ; j < n ; j += 1){
                    if(vals[j] == vals[i]){
                        continue;
                    }
                    ans += pref[j][3-vals[i]-vals[j]];
                    if(2*j-i < n && vals[2*j-i] == 3-vals[i]-vals[j]){
                        ans -= 1;
                    }
                }
            }
            cout << ans << endl;
        }