#include<stdio.h>
struct fibonacci{
    int n;
    int result;
};
int fibonacci(int n){
    if(n == 0)
    return 0;
    else if(n==1)
    return 1;
    else 
    return fibonacci(n-1)+fibonacci(n-2);
}
int main(){
    struct Fibonacci fib;
    scanf("%d", &fib.n);
     if(fib.n<0){
         printf("Invalid input\n");
     }else if (fib.n>20){
         printf("Input out  of range\n");
     }else{
         fib.result = fibonacci(fib.n);
         printf("%d\n",fib.result);
     }
    return 0;
}