import java.math.BigInteger; import java.util.Scanner; public class Main { public static void main(String[] args) { Scanner sc=new Scanner(System.in); while(sc.hasNext()){ int N=sc.nextInt(); int[]a; if(N<=3){ a=new int[3]; a[0]=2;a[1]=4;a[2]=7; System.out.println(a[N-1]); } else{ a=new int[N]; a[0]=2;a[1]=4;a[2]=7; for (int i = 3; i <N; i++) { a[i]=a[i-1]+a[i-2]+a[i-3]; } System.out.println(a[N-1]); } } } }
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