#include<stdio.h>

int main(void)

{

    long long  i,n,narr[55];

    narr[1]=1;narr[2]=2;narr[3]=3;

    for(i=4;i<=50;i++)

    {

        narr[i]=narr[i-1]+narr[i-2];

    }

    while(scanf("%d",&n)!=EOF)

    {

        printf("%lld\n",narr[n]);

    }

    return 0;

}