#include <bits/stdc++.h>
using namespace std;

int main() {
	// max distance between same element
	vector<int> arr={1,1,2,2,2,1};
	unordered_map<int,int> ok;
	int dist=0;
	for(int i=0;i<arr.size();i++){
		if(ok.find(arr[i])!=ok.end()){
			dist=max(dist,i-ok[arr[i]]);
		}else{
				ok[arr[i]]=i;
		}
	
	}
	cout<<dist;
	return 0;
}