```#include <bits/stdc++.h>
using namespace std;
int main() {
    int n;
    scanf("%d", &n);
    char s[5003];
    scanf("%s", s);
    int k[2];
    int sum[5005];
    sum[0] = 1;
    for(int i = 1 ; i < n ; i++) {
        sum[i] = sum[i - 1] + 1;
        int cc = 1;
        for(int g = i - 1 ; g >= 0 ; g--) {
            if(s[i] == s[g]) {
                cc++;
            } else {
                if(sum[g] + (cc + 1) * cc / 2 > sum[i])
                    sum[i] = sum[g] + (cc + 1) * cc / 2;
            }
        }
        if(sum[i] < (cc + 1) * cc / 2) {
            sum[i] = (cc + 1) * cc / 2;
        }
    }
    printf("%d\n", sum[n - 1]);
}