#include <iostream>
using namespace std;
int main() {
int n, h=0, k=0;
cin >> n;
int A[n];
for ( int i = 0; i < n; i++ ) {
cin >> A[i];
}
for ( int i = 0; i < n; i++ ) {
if ( A[n-1] == A[i] ) {
int t = 1;
for ( int j = i + 1; j < n - 1; j++ ) {
if ( A[j] != A[ n - 1 - t ] ) {
k++;
break;
}
t++;
}
if ( k == 0 ) {
h = i;
break;
}
else k = 0;
}
}
cout << h;
return 0;
}
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