#include<bits/stdc++.h>
#define ios std::ios::sync_with_stdio(false)
#define sd(n) scanf("%d",&n)
#define sdd(n,m) scanf("%d%d",&n,&m)
#define sddd(n,m,k) scanf("%d%d%d",&n,&m,&k)
#define pd(n) printf("%d\n", (n))
#define pdd(n,m) printf("%d %d\n", n, m)
#define pld(n) printf("%lld\n", n)
#define pldd(n,m) printf("%lld %lld\n", n, m)
#define sld(n) scanf("%lld",&n)
#define sldd(n,m) scanf("%lld%lld",&n,&m)
#define slddd(n,m,k) scanf("%lld%lld%lld",&n,&m,&k)
#define sf(n) scanf("%lf",&n)
#define sff(n,m) scanf("%lf%lf",&n,&m)
#define sfff(n,m,k) scanf("%lf%lf%lf",&n,&m,&k)
#define rep(i,a,n) for (int i=a;i<=n;i++)
#define per(i,n,a) for (int i=n;i>=a;i--)
#define mm(a,n) memset(a, n, sizeof(a))
#define pb push_back
#define all(x) (x).begin(),(x).end()
#define fi first
#define se second
#define il inline
#define int long long
#define ll long long
#define ull unsigned long long
#define MOD 1000000007
#define pi 3.14159265358979323
#define debug(x) 			  cout <<#x<<": "<<x<<endl;
#define debug2(x, y)          cout <<#x<<": "<<x<<" | "<<#y<<": "<<y<<endl;
#define debug3(x, y, z)       cout <<#x<<": "<<x<<" | "<<#y<<": "<<y<<" | "<<#z<<": "<<z<<endl;
#define debug4(a, b, c, d)    cout <<#a<<": "<<a<<" | "<<#b<<": "<<b<<" | "<<#c<<": "<<c<<" | "<<#d<<": "<<d<<endl;
using namespace std;
const ll INF (0x3f3f3f3f3f3f3f3fll);
const int inf (0x3f3f3f3f);
template<typename T>void read(T &res){bool flag=false;char ch;while(!isdigit(ch=getchar()))(ch=='-')&&(flag=true);
for(res=ch-48;isdigit(ch=getchar());res=(res<<1)+(res<<3)+ch - 48);flag&&(res=-res);}
template<typename T>void Out(T x){if(x<0)putchar('-'),x=-x;if(x>9)Out(x/10);putchar(x%10+'0');}
ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}
ll lcm(ll a,ll b){return a*b/gcd(a,b);}
ll pow_mod(ll x,ll n,ll mod){ll res=1;while(n){if(n&1)res=res*x%mod;x=x*x%mod;n>>=1;}return res;}
ll fact_pow(ll n,ll p){ll res=0;while(n){n/=p;res+=n;}return res;}
ll mult(ll a,ll b,ll p){a%=p;b%=p;ll r=0,v=a;while(b){if(b&1){r+=v;if(r>p)r-=p;}v<<=1;if(v>p)v-=p;b>>=1;}return r;}
ll quick_pow(ll a,ll b,ll p){ll r=1,v=a%p;while(b){if(b&1)r=mult(r,v,p);v=mult(v,v,p);b>>=1;}return r;}
bool CH(ll a,ll n,ll x,ll t)
{ll r=quick_pow(a,x,n);ll z=r;for(ll i=1;i<=t;i++){r=mult(r,r,n);if(r==1&&z!=1&&z!=n-1)return true;z=r;}return r!=1;}
bool Miller_Rabin(ll n)
{if(n<2)return false;if(n==2)return true;if(!(n&1))return false;ll x=n-1,t=0;while(!(x&1)){x>>=1;t++;}srand(time(NULL));
ll o=8;for(ll i=0;i<o;i++){ll a=rand()%(n-1)+1;if(CH(a,n,x,t))return false;}return true;}
void exgcd(ll a,ll b ,ll &x,ll &y){if(!b){x=1,y=0;return;}exgcd(b,a%b,x,y);ll t=x;x=y,y=t-(a/b)*y;}
ll inv(ll a,ll b){ll x,y;return exgcd(a,b,x,y),(x%b+b)%b;}
ll crt(ll x,ll p,ll mod){return inv(p/mod,mod)*(p/mod)*x;}
ll fac(ll x,ll a,ll b)
{if(!x)return 1;ll ans=1;for(ll i=1;i<=b;i++)if(i%a)ans*=i,ans%=b;
ans=pow_mod(ans,x/b,b);for(ll i=1;i<=x%b;i++)if(i%a)ans*=i,ans%=b;return ans*fac(x/a,a,b)%b;}
ll C(ll n,ll m,ll a,ll b)
{ll N=fac(n,a,b),M=fac(m,a,b),Z=fac(n-m,a,b),sum=0,i;for(i=n;i;i=i/a)sum+=i/a;
for(i=m;i;i=i/a)sum-=i/a;for(i=n-m;i;i=i/a)sum-=i/a;return N*pow_mod(a,sum,b)%b*inv(M,b)%b*inv(Z,b)%b;}
ll exlucas(ll n,ll m,ll p)
{ll t=p,ans=0,i;for(i=2;i*i<=p;i++){ll k=1;while(t%i==0){k*=i,t/=i;}
ans+=crt(C(n,m,i,k),p,k),ans%=p;}if(t>1)ans+=crt(C(n,m,t,t),p,t),ans%=p;return ans % p;}
int prime[100000],minprime[100000];
void euler(int n)
{int c=0,i,j;for(i=2;i<=n;i++){if(!minprime[i])prime[++c]=i,minprime[i]=i;for(j=1;j<=c&&i*prime[j]<=n;j++)
{minprime[i*prime[j]]=prime[j];if(i%prime[j]==0)break;}}}
struct Tree{ll l,r,sum,lazy,maxn,minn;}tree[100000];
il void push_up(ll rt)
{tree[rt].sum=tree[rt<<1].sum+tree[rt<<1|1].sum;
tree[rt].maxn=max(tree[rt<<1].maxn,tree[rt<<1|1].maxn);
tree[rt].minn=min(tree[rt<<1].minn,tree[rt<<1|1].minn);}
il void push_down(ll rt , ll length)
{if(tree[rt].lazy){tree[rt<<1].lazy+=tree[rt].lazy;tree[rt<<1|1].lazy+=tree[rt].lazy;
tree[rt<<1].sum+=(length-(length>>1))*tree[rt].lazy;tree[rt<<1|1].sum+=(length>>1)*tree[rt].lazy;
tree[rt<<1].minn+=tree[rt].lazy;tree[rt<<1|1].minn+=tree[rt].lazy;
tree[rt<<1].maxn+=tree[rt].lazy;tree[rt<<1|1].maxn+=tree[rt].lazy;tree[rt].lazy=0;}}
il void build(ll l , ll r , ll rt , ll *aa)
{tree[rt].lazy=0;tree[rt].l=l;tree[rt].r=r;if(l==r)
{tree[rt].sum=aa[l];tree[rt].minn=tree[rt].sum;tree[rt].maxn=tree[rt].sum;return;}
ll mid=(l+r)>>1;build(l,mid,rt<<1,aa);build(mid+1,r,rt<<1|1,aa);push_up(rt);}
il void update_range(ll L , ll R , ll key , ll rt)
{if(tree[rt].r<L||tree[rt].l>R)return;if(L<=tree[rt].l&&R>=tree[rt].r){tree[rt].sum+=(tree[rt].r-tree[rt].l+1)*key;
tree[rt].minn+=key;tree[rt].maxn+=key;tree[rt].lazy+=key;return;}push_down(rt,tree[rt].r-tree[rt].l+1);
ll mid=(tree[rt].r+tree[rt].l)>>1;if(L<=mid)update_range(L,R,key,rt << 1);
if(R>mid)update_range(L,R,key,rt << 1 | 1);push_up(rt);}
il ll query_range(ll L, ll R, ll rt)
{if(L<=tree[rt].l&&R>=tree[rt].r){return tree[rt].sum;}push_down(rt,tree[rt].r-tree[rt].l+1);
ll mid=(tree[rt].r+tree[rt].l)>>1;ll ans=0;if(L<=mid)ans+=query_range(L,R,rt << 1);
if(R>mid)ans+=query_range(L,R,rt << 1 | 1);return ans;}
il ll query_min(ll L,ll R,ll rt)
{if(L<=tree[rt].l&&R>=tree[rt].r){return tree[rt].minn;}push_down(rt,tree[rt].r-tree[rt].l+1);
ll mid=(tree[rt].r+tree[rt].l)>>1;ll ans=(0x3f3f3f3f3f3f3f3fll);if(L<=mid)ans=min(ans,query_min(L,R,rt << 1));
if(R>mid)ans=min(ans,query_min(L,R,rt << 1 | 1));return ans;}
il ll query_max(ll L, ll R, ll rt)
{if(L<=tree[rt].l&&R>=tree[rt].r){return tree[rt].maxn;}push_down(rt,tree[rt].r-tree[rt].l+1);
ll mid=(tree[rt].r+tree[rt].l)>>1;ll ans=-(0x3f3f3f3f3f3f3f3fll);if(L<=mid)ans=max(ans,query_max(L,R,rt << 1));
if(R>mid)ans=max(ans,query_max(L,R,rt << 1 | 1));return ans;}

const int N = 2e5 + 10; 
const ll mod = 998244353 ;
int n , a[N] ;
map<int , ll> dp[N] ;
void solve()
{
	rep(i , 1 , n)  dp[i][1] = a[i] ;
	rep(i , 3 , n)
	{
		rep(j , max(2LL , i / 2 - 3) , min(n , i / 2 + 3))
		{
		   ll max1 = -1e18 ; 
		   rep(k , max(1LL , i - 5) , i - 2)
		   {
		  	 if(dp[k].count(j - 1) == 0)  continue ;
		  	 max1 = max(max1 , dp[k][j - 1] + a[i]) ;
		   }
		   if(max1 < -1e17)  continue ;
		   dp[i][j] = max1 ; 	
		}  
	}
	ll ans = -1e18 ;
	rep(i , max(1LL , n - 10) , n)  
	  if(dp[i].count(n / 2))
        ans = max(ans , dp[i][n / 2]) ;
	cout << ans << '\n';
}
string s;
int r[4007],b[4007],g[4007];
signed main(){
    ios; 
    int n;
    cin>>n;
    cin>>s;
    if(s[0]=='R')
        r[0]=1;
    else if(s[0]=='B')
        b[0]=1;
    else if(s[0]=='G')
        g[0]=1;
    for(int i=1;i<n;++i){
        r[i]=r[i-1];
        b[i]=b[i-1];
        g[i]=g[i-1];
        if(s[i]=='R')
            ++r[i];
        else if(s[i]=='B')
            ++b[i];
        else if(s[i]=='G')
            ++g[i];
    }
    int flag=0,flag2=0;
    long long sum=0;
    for(int i=0;i<n-2;++i){
        flag=0;
        if(s[i]=='R')
            flag=1;
        else if(s[i]=='B')
            flag=2;
        else if(s[i]=='G')
            flag=3;
        for(int j=i+1;j<n-1;++j){
            flag2=0;
            if(s[i]==s[j])
                continue;
            if(s[j]=='R')
                flag2=1;
            else if(s[j]=='B')
                flag2=2;
            else if(s[j]=='G')
                flag2=3;
            if(flag==1&&flag2==2){
                sum+=g[n-1]-g[j];
                if(j+j-i<n&&s[j+j-i]=='G')
                    --sum;
            }
            else if(flag==1&&flag2==3){
                sum+=b[n-1]-b[j];
                if(j+j-i<n&&s[j+j-i]=='B')
                    --sum;
            }
            else if(flag==2&&flag2==1){
                sum+=g[n-1]-g[j];
                if(j+j-i<n&&s[j+j-i]=='G')
                    --sum;
            }
            else if(flag==2&&flag2==3){
                sum+=r[n-1]-r[j];
                if(j+j-i<n&&s[j+j-i]=='R')
                    --sum;
            }
            else if(flag==3&&flag2==1){
                sum+=b[n-1]-b[j];
                if(j+j-i<n&&s[j+j-i]=='B')
                    --sum;
            }
            else if(flag==3&&flag2==2){
                sum+=r[n-1]-r[j];
                if(j+j-i<n&&s[j+j-i]=='R')
                    --sum;
            }
        }
    }
    cout<<sum;
    return 0;
}




Measured memory_bytes: 13080