#简单的递归

int main()
{
    int n;
    scanf("%d", &n);
    int a=1,b=1,sum=0,i;
    if(n<=2)
    {
        printf("1");
        return 0;
    }
    for(i=2; i<n; i++)
    {
        sum = a+b;
        a = b;
        b = sum;
    }
    printf("%d", sum);
    return 0;
}