[sicily]1561. PRIME

1561. PRIME

Constraints

Time Limit: 1 secs, Memory Limit: 32 MB

Description

A prime number is a natural number which has exactly two distinct natural number divisors: 1 and itself. The first prime number is 2. Can you write a program that computes the nth prime number, given a number n <= 10000?

Input

The input contains just one number which is the number n as described above.
The maximum value of n is 10000.

Output

The output consists of a single line with an integer that is the nth prime number.

Sample Input

30

Sample Output

113

求第n 个素数，使用筛法即可。代码如下：

#include <iostream>#include <cstring>#include <cmath>using namespace std;#define N 1299710bool prime[N];int main(){    memset(prime, true, sizeof(prime));    for(int i=2; i<N; i++)        if(prime[i])            for(int j=2*i; j<N; j=j+i)                prime[j] = false;    int n,index=1,count=0;     cin>>n;    while(count<n)    {        index++;        if(prime[index])            count++;    }    cout<<index<<endl;   // system("pause");    return 0;   }