/*#include <stdio.h>
int memo [15][15]={0};
int SuperSum(int k,int n)
{
if(memo[k][n]!=0) return memo [k][n];
if(k==0) return n;
if(n==0) return 0;
return memo[k][n]=SuperSum(k,n-1)+SuperSum(k-1,n);
}
int main()
{
int k,n;
while(scanf("%d %d", &k,&n)!=EOF)
printf("%d\n",SuperSum(k,n));
}
f(1) 1
f(2) 2
f(3) 4
f(4) 7
f(5) 13
f(6) 24
..
f(n) ->
*/
#include <stdio.h>
int main()
{
int n;
scanf("%d",&n);
printf("%d",f(n));
}