///...................SUBHASHIS MOLLICK...................///
///.....DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING....///
///.............ISLAMIC UNIVERSITY,BANGLADESH.............///
///....................SESSION-(14-15)....................///
#include<bits/stdc++.h>
using namespace std;
#define sf(a) scanf("%d",&a)
#define sf2(a,b) scanf("%d %d",&a,&b)
#define sf3(a,b,c) scanf("%d %d %d",&a,&b,&c)
#define pf(a) printf("%d",a)
#define pf2(a,b) printf("%d %d",a,b)
#define pf3(a,b,c) printf("%d %d %d",a,b,c)
#define sfl(a) scanf("%lld",&a)
#define sfl2(a,b) scanf("%lld %lld",&a,&b)
#define sfl3(a,b,c) scanf("%lld %lld %lld",&a,&b,&c)
#define pfl(a) printf("%lld",a)
#define pfl2(a,b) printf("%lld %lld",a,b)
#define pfl3(a,b,c) printf("%lld %lld %lld",a,b,c)
#define nl printf("\n")
#define   timesave              ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
#define ll long long
#define pb push_back
#define MPI map<int,int>mp;
#define fr(i,n) for(i=0;i<n;i++)
#define fr1(i,n) for(i=1;i<=n;i++)
#define frl(i,a,b) for(i=a;i<=b;i++)
#define tz 100000
#define clr0(a) memset(a,0,sizeof(a))
#define clr1(a) memset(a,-1,sizeof(a))
/*primes in range 1 - n
1 - 100(1e2) -> 25 pimes
1 - 1000(1e3) -> 168 primes
1 - 10000(1e4) -> 1229 primes
1 - 100000(1e5) -> 9592 primes
1 - 1000000(1e6) -> 78498 primes
1 - 10000000(1e7) -> 664579 primes
large primes ->
104729 1299709 15485863 179424673 2147483647 32416190071 112272535095293 48112959837082048697
*/
//freopen("Input.txt","r",stdin);
//freopen("Output.txt","w",stdout);
//const int fx[]={+1,-1,+0,+0};
//const int fy[]={+0,+0,+1,-1};
//const int fx[]={+0,+0,+1,-1,-1,+1,-1,+1};   // Kings Move
//const int fy[]={-1,+1,+0,+0,+1,+1,-1,-1};  // Kings Move
//const int fx[]={-2, -2, -1, -1,  1,  1,  2,  2};  // Knights Move
//const int fy[]={-1,  1, -2,  2, -2,  2, -1,  1}; // Knights Move
int red[4005],grn[4005],blue[4005];
main()
{
    timesave;
    int n,i,j,k,x;
    cin>>n;
    string s;
    cin>>s;
    ll ans=0;
    if(s[0]=='R')
    {
        red[0]=1;
        grn[0]=0;
        blue[0]=0;
    }
    if(s[0]=='G')
    {
        red[0]=0;
        grn[0]=1;
        blue[0]=0;
    }
    if(s[0]=='B')
    {
        red[0]=0;
        grn[0]=0;
        blue[0]=1;
    }
    for(i=1;i<n;i++)
    {
        if(s[i]=='R')
        {
            red[i]=red[i-1]+1;
            grn[i]=grn[i-1];
            blue[i]=blue[i-1];
        }
        else if(s[i]=='G')
        {
            red[i]=red[i-1];
            grn[i]=grn[i-1]+1;
            blue[i]=blue[i-1];
        }
        else if(s[i]=='B')
        {
            red[i]=red[i-1];
            grn[i]=grn[i-1];
            blue[i]=blue[i-1]+1;
        }
    }
    for(i=0;i<n-1;i++)
    {
        if(s[i]=='R')
        {
            for(j=i+1;j<n;j++)
            {
                if(s[j]=='G')
                {
                    x=j-i;
                    if(j+x<n&&s[j+x]=='B')
                        ans=ans+(blue[n-1]-blue[j]-1);
                    else
                        ans=ans+(blue[n-1]-blue[j]);
                }
                else if(s[j]=='B')
                {
                     x=j-i;
                    if(j+x<n&&s[j+x]=='G')
                        ans=ans+(grn[n-1]-grn[j]-1);
                    else
                        ans=ans+(grn[n-1]-grn[j]);
                }
            }
        }
        else if(s[i]=='G')
        {
            for(j=i+1;j<n;j++)
            {
                if(s[j]=='R')
                {
                    x=j-i;
                    if(j+x<n&&s[j+x]=='B')
                        ans=ans+(blue[n-1]-blue[j]-1);
                    else
                        ans=ans+(blue[n-1]-blue[j]);
                }
                else if(s[j]=='B')
                {
                    x=j-i;
                    if(j+x<n&&s[j+x]=='R')
                        ans=ans+(red[n-1]-red[j]-1);
                    else
                        ans=ans+(red[n-1]-red[j]);
                }
            }
        }
        else if(s[i]=='B')
        {
            for(j=i+1;j<n;j++)
            {
                if(s[j]=='G')
                {
                    x=j-i;
                    if(j+x<n&&s[j+x]=='R')
                        ans=ans+(red[n-1]-red[j]-1);
                    else
                        ans=ans+(red[n-1]-red[j]);
                }
                else if(s[j]=='R')
                {
                     x=j-i;
                    if(j+x<n&&s[j+x]=='G')
                        ans=ans+(grn[n-1]-grn[j]-1);
                    else
                        ans=ans+(grn[n-1]-grn[j]);
                }
            }
        }
    }
    cout<<ans<<endl;
}






Measured memory_bytes: 3668