#include<bits/stdc++.h>
using namespace std;

typedef long long ll;
typedef pair<int,int> P;

#define p_ary(ary,a,b) do { cout << "["; for (int count = (a);count < (b);++count) cout << ary[count] << ((b)-1 == count ? "" : ", "); cout << "]\n"; } while(0)
#define p_map(map,it) do {cout << "{";for (auto (it) = map.begin();;++(it)) {if ((it) == map.end()) {cout << "}\n";break;}else cout << "" << (it)->first << "=>" << (it)->second << ", ";}}while(0)

template<typename T1,typename T2>ostream& operator<<(ostream& os,const pair<T1,T2>& a) {os << "(" << a.first << ", " << a.second << ")";return os;}

const char newl = '\n';

int main() {
    ll n;
    string s;
    cin >> n >> s;
    ll a[3] = {0,0,0};
    for (int i = 0;i < n;++i) {
        if (s[i] == 'R') a[0]++;
        else if (s[i] == 'G') a[1]++;
        else a[2]++;
    }
    ll ans = a[0]*a[1]*a[2];
    for (int i = 1;i < n;++i) {
        for (int j = 0;j < n;++j) {
            if (j+i+i >= n) break;
            if (s[j] != s[j+i] && s[j+i] != s[j+i+i] && s[j] != s[j+i+i]) ans--;
        }
    }
    cout << ans << endl;
}