1 2 3 4 5 6 7
4-5-3-6-2-7-1
答案是(n-1)/2
#include<cstdio>
using namespace std;
int n;
int main(){
scanf("%d",&n);
printf("%d\n",(n-1)/2);
return 0;
}
【推导】Codeforces Round #411 (Div. 1) A. Find Amir
原文：http://www.cnblogs.com/autsky-jadek/p/6815489.html