#include<math.h>
#include<stdio.h>
double fun(int n)
{int i,j;
double s=0;
for(i=3;i<=n;i++)
{for(j=2;j<n;j++)
if(i%j==0)
break;
s=s+sqrt(i);}
return s;
}
main()
{
int n;
double sum;
printf("\n\nInput n:");
scanf("%d",&n);
sum=fun(n);
printf("\n\nsum=%f\n\n",sum);
}