You should generate a sequence of positive integers of length n.

Of course,this sequence needs to meet some requirements.

• ∀ i∈[1,n]  ai​>1

• ∀ i∈[2,n]  gcd(ai−1​,ai​)=1

• a1​=k(k>1)

gcd(x,y) means the greatest common divisor of x and y.

You need to find the minimum value of

输入格式:

The only line contains two integers n,k

2≤n≤10^8,2≤k≤10^8

输出格式:

One integer — the answer to the problem.

输入样例:

2 5

样例">样例">输出样例:

7

题意： 

给出一个n,k ，求出一串序列，序列的第一个元素为k，序列满足相邻两个数互质，且序列的总和最小，输出总和

题解：

先求出第二个数，第二个数为最小的与k互质的数，如果k为奇数，那么第二个数必定为偶数，那么后面的序列为3232... 如果k为偶数，那么第二个数必定为奇数，那么后面的序列为2323...

#include
#include
using namespace std;
typedef long long ll ;
const int N = 1e8+10;
int n , k ;
int a[2] = {2,3};
int main()
{cin >> n >> k ;ll res = k ;if(k%2){ //第二个数res += 2;}else{for(int i = 3 ; i < k ; i++){if(__gcd(k,i)==1){ res += i ; break;}}} if( k%2 ) //k为奇数for(int i = 1 ; i <= n-2; i++ )res += a[i%2];else //k为偶数for(int i = 0 ; i < n-2; i++ )res += a[i%2];cout << res << endl;return 0;
}