#include <cstdio>

int N;
long long dp[51];

int main(){
    scanf("%d", &N);

    dp[0] = 1ll;
    for(int i=1;i<=N;i++){
        dp[i] += dp[i-1];
        if(i-2 >= 0){dp[i] += dp[i-2];}
    }

    printf("%lld\n", dp[N]);
}