#include <stdio.h>
#include <math.h>
void main()
{ int i,n=0,j;
for (i=667;i<=777;i+=2)
    {    for (j=2;j<=sqrt(i);j++)  /* 判断i是不是素数*/
           if (i%j==0) break;
         if (j>sqrt(i)) {n++; }
     }
    printf("\n%d",n);
 }