#include <algorithm>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <deque>
#include <queue>
#include <stack>
#include <vector>
#include <unordered_map>
#include <unordered_set>
#include <map>
#include <set>
using namespace std;

#define rep(i, n)     for (int(i) = int(1); int(i) <= int(n); ++i)
#define repd(i, n)    for (int(i) = int(n); int(i) >= int(1); --i)
#define FOR(i, l, r)  for (int(i) = int(l); int(i) <= int(r); ++i)
#define FORD(i, l, r) for (int(i) = int(r); int(i) >= int(l); --i)
#define hashmap unordered_map
#define hashset unordered_set
#define fi first
#define se second
#define pb push_back
#define mp make_pair
#define mt make_tuple
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define itr iterator
#define rtr reverse_iterator

typedef long long       ll;     typedef unsigned long long  ull;
typedef pair<int, int>  pi;     typedef pair<ll, ll>    pll;
typedef set<int>        si;     typedef vector<si>      vsi;
typedef set<ll>         sll;    typedef vector<sll>     vsll;
typedef set<pi>         spi;    typedef vector<spi>     vspi;
typedef set<pll>        spll;   typedef vector<spll>    vspll;
typedef vector<bool>    vb;     typedef vector<vb>      vmb;
typedef vector<char>    vc;     typedef vector<vc>      vmc;
typedef vector<int>     vi;     typedef vector<vi>      vmi;    
typedef vector<ll>      vll;    typedef vector<vll>     vmll;
typedef vector<pi>      vpi;    typedef vector<vpi>     vmpi;
typedef vector<pll>     vpll;   typedef vector<vpll>    vmpll;

inline int readInt()       {char c;while(c=getchar(),c!='-'&&(c<'0'||c>'9'));bool sign=(c=='-');if(sign)c=getchar();int n=c-'0';while(c=getchar(),c>='0'&&c<='9')n=10*n+c-'0';return(!sign)?n:-n;}
inline ll readLong()       {char c;while(c=getchar(),c!='-'&&(c<'0'||c>'9'));bool sign=(c=='-');if(sign)c=getchar();ll  n=c-'0';while(c=getchar(),c>='0'&&c<='9')n=10*n+c-'0';return(!sign)?n:-n;}
inline void getInt(int& n) {char c;while(c=getchar(),c!='-'&&(c<'0'||c>'9'));bool sign=(c=='-');if(sign)c=getchar();    n=c-'0';while(c=getchar(),c>='0'&&c<='9')n=10*n+c-'0';      if(sign)n=-n;}
inline void getLong(ll& n) {char c;while(c=getchar(),c!='-'&&(c<'0'||c>'9'));bool sign=(c=='-');if(sign)c=getchar();    n=c-'0';while(c=getchar(),c>='0'&&c<='9')n=10*n+c-'0';      if(sign)n=-n;}
inline string readString() {char c;while(c=getchar(),c==' '||c=='\n'||c=='\t');string s({c});while(c=getchar(),c!=' '&&c!='\n'&&c!='\t')s+=c;return s;}
char bufWrite[20];
template<typename T>inline void writeInt(T x)               {if(x<0)putchar('-'),x=-x;char*bufPos=bufWrite;do{*bufPos++=x%10+'0';}while(x/=10);do{putchar(*--bufPos);}while(bufPos>bufWrite);}
template<typename T>inline void printInt(T x, char c = EOF) {if(x<0)putchar('-'),x=-x;char*bufPos=bufWrite;do{*bufPos++=x%10+'0';}while(x/=10);do{putchar(*--bufPos);}while(bufPos>bufWrite);if(c!=EOF)putchar(c);}
template<typename T>inline T gcd(T a,T b){while(b!=0)swap(b,a%=b);return a;}
template<typename T>inline T lcm(T a,T b){return a/gcd(a,b)*b;}
template<typename T>inline tuple<T,T,T>extgcd(T a,T b){if(!a)return mt(b,0,1);T g,x,y;tie(g,x,y)=extgcd(b%a,a);return mt(g,(y-(b/a)*x),x);}
template <class T> T    bitGet    (T  x, int bit)           { return T(1) & (x >> (bit - 1)); }
template <class T> void bitSet    (T &x, int bit)           { x |=  (T(1) << (bit - 1)); }
template <class T> void bitReset  (T &x, int bit)           { x &= ~(T(1) << (bit - 1)); }
template <class T> void bitFlip   (T &x, int bit)           { x ^=  (T(1) << (bit - 1)); }
template <class T> void bitMake   (T &x, int bit, bool val) { x ^=  (T(1) << (bit - 1)) & (-val ^ x); }
/// ======================================================================
/// =====================================================================   =

int query()
{


    return 0;
}

int main()
{
    int n = readInt();
    string s = readString();

    int r = 0, b = 0, g = 0;
    for (const char c : s)
    {
        r += c == 'R';
        b += c == 'B';
        g += c == 'G';
    }

    ll res = 1LL * r * b * g;
    for (int j = 0; j < n; ++j)
        for (int l = j - 1, r = j + 1; 0 <= l && r <= n - 1; --l, ++r)
            res -= (s[l] != s[j] && s[j] != s[r] && s[l] != s[r]);
            

    cout << res;
    return 0;
}

Measured memory_bytes: 3632