#include <iostream>
#include <algorithm>
#include <iterator>
#include <math.h>
#include <vector>
#include <set>
using namespace std;
int main() {
int n;
string s;
cin >> n >> s;
char x = s[0];
char y = s[n - 1];
int c1 = 0, c2 = 0;
int c3 = 0, c4 = 0;
for (int i = 0; i < n; i++) {
if (s[i] == x) {
c1 = i;
}
}
for (int j = n - 1; j >= c1; j--) {
if (s[j] == y) {
c2 = j;
}
}
for (int j = n - 1; j >= 0; j--) {
if (s[j] == y) {
c3 = j;
}
}
for (int i = 0; i <= c3; i++) {
if (s[i] == x) {
c4 = i;
}
}
cout << max(n - (c2 - c1 + 1), n - (c3 - c4 + 1));
return 0;
}
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