/*
 * FileName:     no_786_fix
 * CreatedDate:  2020-05-21 22:04:08 +0900
 * LastModified: 2020-05-21 22:16:06 +0900
 */

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

int main(void){
    int n;
    scanf("%d",&n);
    long long int *dp = malloc(sizeof(int)*(n+1));
    dp[2]=2;
    dp[1]=1;
    for(int i=3;i<n+1;i++){
        dp[i] = dp[i-1] + dp[i-2];
    }
    printf("%lld\n",dp[n]);
    free(dp);
    return 0;
}