#include <stdio.h>
int n, k, ans;
void solve(int x, int y, int z)
{
    if( z == 3 ) return;
    if( x == n )
    {
        if( y == k and z < 2 ) ans++;
        return;
    }
    solve(x+1, y+1, z+1);
    solve(x+1, y, 0);
}
int main()
{

    scanf("%d%d", &n, &k);
    solve(0, 0, 1);
    printf("%d\n", ans);
    return 0;
}