/*
 * FileName:     no_786
 * CreatedDate:  2020-04-23 01:21:30 +0900
 * LastModified: 2020-04-23 11:35:53 +0900
 */

#include <stdio.h>

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