#include<iostream>
#include<iomanip>
#include<cstdio>
#include<algorithm>
#include<cstring>
#include<cmath>
#include<queue>
#include<stack>
#include<vector>
#include<string>
#include<map>
#include<set>
#include<ctime>
#define ll  long long
#define ull unsigned long long
using namespace std;

int a[300010];
 
int main () {
    //ios::sync_with_stdio(false);
    int n;
    cin >> n;
 
    for (int i = 0; i < n; ++i) {
        scanf("%d", &a[i]);
    }
    //int len = 0;
    //bool aa = 0;
    int j = n - 1;
    int i = 0;
    int temp1 = 0;
    int temp2 = 0;
    for (int i = 0 , j = n - 1; i < j; ) {
        if (a[i] != a[j]){
            temp1 = j - i;
            break;
        }
        else {
            i++;
        }
    }
    for (int i = 0 , j = n - 1; i < j; ) {
            j--;
        if (a[i] != a[j]){
            temp2 = j - i;
            break;
        }
    }
    temp1 = max(temp1, temp2);
    //temp = max(temp, n - 1 - temp);
    printf("%d\n", temp1);
}