HDOJ 2136

#include <stdio.h>

int main()
{
        const int max = 1000001;
        int *lpf = new int[max];
        int c = 2,n;
        for(int i = 0;i < max;++i) lpf[i] = 0;
        lpf[2] = 1;
        for(int i = 4;i < max;i += 2)
        {
                lpf[i] = lpf[2];
        }
        for(int i = 3;i < max;++i)
        {
                if(lpf[i]) continue;
                lpf[i] = c++;
                for(int j = (i<<1);j < max;j += i)
                {
                        lpf[j] = lpf[i];
                }
        }
        while(scanf("%d",&n) != EOF)
                printf("%d\n",lpf[n]);

        return 0;
}