uva 10820

欧拉函数

#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <cstring>
#include <algorithm>
#define maxn 50010
#define INF 0x7fffffff
#define ull unsigned long long
using namespace std;

int prime[maxn];
int n;
void init()
{
    memset(prime, 0, sizeof(prime));
    prime[1] = 1;
    for(int i  = 2; i < maxn; i++)
        if(!prime[i])
            for(int j = i ; j < maxn; j+=i)
            {
                if(!prime[j]) prime[j] = j;
                prime[j] -= prime[j] / i;
            }
}
int main()
{
    init();
    for(int i = 2; i < maxn; i++)
        prime[i] += prime[i-1];
    while(scanf("%d", &n) != EOF && n)
    {
        printf("%d\n", prime[n]*2-1);
    }
    return 0;
}