#include<bits/stdc++.h>
using namespace std;
#define int long long
int ans,r[100010],g[100010],b[100010],n;
char s[100010];
signed main() {
	cin>>n;
	for(int i=1; i<=n; i++) {
		cin>>s[i];
		b[i]=b[i-1];
		g[i]=g[i-1];
		r[i]=r[i-1];
		if(s[i]=='R') {
			r[i]++;
		}
		if(s[i]=='G') {
			g[i]++;
		}
		if(s[i]=='B') {
			b[i]++;
		}
	}
	for(int i=2; i<=n-1; i++) {
		if(s[i]=='R') {
			ans+=g[i]*(b[n]-b[i]);
			ans+=b[i]*(g[n]-g[i]);
		}
		if(s[i]=='G') {
			ans+=r[i]*(b[n]-b[i]);
			ans+=b[i]*(r[n]-r[i]);
		}
		if(s[i]=='B') {
			ans+=g[i]*(r[n]-r[i]);
			ans+=r[i]*(g[n]-g[i]);
		}
		for(int j=1; j<=n; j++) {
			int sb1=i-j,sb2=i+j,sb3=n+1;
			if(sb1<=0||sb2>=sb3) {
				break;
			}
			if(s[sb1]!=s[sb2]&&s[sb1]!=s[i]&&s[i]!=s[sb2])ans--;
		}
	}
	cout<<ans;
	return 0;
}