#include<stdio.h>

int main()
{
    freopen("nunta.in","r",stdin);
    freopen("nunta.out","w",stdout);
    int n;
    scanf("%d",&n);
    long long a=1,b=1,c;
    if(n==1)
     {printf("1\n");
      return 0;
     }
    for(int i=2;i<=n;i++)
     {
      c=a+b;
      a=b;
      b=c;
     }
    printf("%lld\n",c);
    return 0;
}