import std.stdio, std.string, std.conv, std.range;
import std.algorithm, std.array, std.typecons, std.container;
import std.math, std.numeric, std.random, core.bitop;

enum inf = 1_001_001_001;
enum infl = 1_001_001_001_001_001_001L;


void main() {
    int N;
    string s;

    scan(N);
    scan(s);

    auto r = new long[](N + 1);
    auto g = new long[](N + 1);
    auto b = new long[](N + 1);

    foreach (i ; 1 .. N + 1) {
        r[i] = r[i - 1] + (s[i - 1] == 'R');
        g[i] = g[i - 1] + (s[i - 1] == 'G');
        b[i] = b[i - 1] + (s[i - 1] == 'B');
    }

    long ans;

    foreach (i ; 0 .. N) {
        if (s[i] == 'R') {
            ans += g[i] * (b[N] - b[i + 1]);
            ans += b[i] * (g[N] - g[i + 1]);
        }
        if (s[i] == 'G') {
            ans += r[i] * (b[N] - b[i + 1]);
            ans += b[i] * (r[N] - r[i + 1]);
        }
        if (s[i] == 'B') {
            ans += r[i] * (g[N] - g[i + 1]);
            ans += g[i] * (r[N] - r[i + 1]);
        }

        foreach (j ; 1 .. N) {
            if (i - j < 0 || i + j >= N) break;
            if (s[i - j] != s[i] && s[i] != s[i + j] && s[i - j] != s[i + j]) {
                ans--;
            }
        }
    }

    writeln(ans);
}



void scan(T...)(ref T args) {
    auto line = readln.split;
    foreach (ref arg; args) {
        arg = line.front.to!(typeof(arg));
        line.popFront;
    }
    assert(line.empty);
}

void fillAll(R, T)(ref R arr, T value) {
    static if (is(typeof(arr[] = value))) {
        arr[] = value;
    }
    else {
        foreach (ref e; arr) {
            fillAll(e, value);
        }
    }
}

bool chmin(T, U...)(ref T x, U args) {
    bool isChanged;
    foreach (arg; args) if (x > arg) {
        x = arg;
        isChanged = true;
    }
    return isChanged;
}

bool chmax(T, U...)(ref T x, U args) {
    bool isChanged;
    foreach (arg; args) if (x < arg) {
        x = arg;
        isChanged = true;
    }
    return isChanged;
}

void yes(bool ok, string y = "Yes", string n = "No") {
    return writeln(ok ? y : n);
}
