#include <stdio.h>

int main(void) {
	int n;
	char s[1000001];
	scanf("%d", &n);
	scanf("%s", &s);
	
	if(n == 1){
		printf("NO\n");
	}
	else if(n == 2){
		if(s[0] == s[1]){
			printf("YES\n");
		}
		else{
			printf("NO\n");
		}
	}
	else if(n == 3){
		if(s[0] == s[2] && s[0] != s[1]){
			printf("NO\n");
		}
		else{
			printf("YES\n");
		}
	}
	else{
		printf("YES\n");
	}

	return 0;
}