#include <stdio.h>

int N;
long long dp[52];

int main() {
    scanf("%d", &N);
    dp[0] = 1;
    for (int i = 0; i < 50; i++) {
        dp[i + 1] += dp[i];
        dp[i + 2] += dp[i];
    }
    printf("%lld\n", dp[N]);
    return 0;
}