#include <stdio.h> //套公式 int main() { int a1 = 2; int n = 0; scanf("%d",&n); //sn=na1+n(n-1)d/2; int sn = 0; sn = n * a1 + n * (n - 1) * 3 / 2; printf("%d\n", sn); return 0; }