#include <stdio.h>
#include <string.h>
int main(){
  int N;
  char S[1000000];
  
  scanf("%d",&N);
  scanf("%s",S);
  
  if(N<=2){
    printf("NO\n");
  }
  else if(strcmp(S,"101")+strcmp(S,"010")==1){
    printf("NO\n");
  }
  else{
    printf("YES\n");
  }
  return 0;
}