#include <stdio.h>
#include <malloc.h>
#include <stdint.h>

int ptns = 0;
int n;
/// <summary>
/// 入力された数字を返す
/// </summary>
/// <returns></returns>
int ReadNum() {
	int negate = 0;
	char c = getchar();
	int num = 0;
	int numCnt = 0;
	while (c != '\n') {
		if (c == '-') {
			negate = 1;
		}
		else {
			num = num * 10 + c - '0';
		}

		c = getchar();
	}
	if (negate == 1) {
		num *= -1;
	}
	return num;
}

void reflex(int* nums,int cnt) {
	if (cnt < n) {
		for (int i = 0;i < 2;i++) {
			nums[cnt] = i;
			reflex(nums,cnt+1);
		}
	}
	if (cnt == n) {
		int ken = 0;
		for (int i = 0;i < n;i++) {
			if (nums[i] == 0) {
				ken++;
				if (ken == 3) return;
			}
			if (nums[i] == 1) {
				ken = 0;
				if (i == 0) return;
				if (nums[i - 1] == 1) return;
			}
		}
		for (int i = 0;i < n;i++) printf("%d", nums[i]);
		printf("\n");
		ptns++;
	}
}

int main() {
	n = ReadNum();
	unsigned int* nums;
	nums = (unsigned int*)malloc(sizeof(unsigned int) * n);
	nums[0] = 1;
	nums[1] = 2;
	nums[2] = 2;
	for (int i = 3;i < n;i++) {
		nums[i] = nums[i - 3] + nums[i - 2];
	}

	printf("%d\n",nums[n-1]);
}