#include<stdio.h>
#include<math.h>
int main()
{int n,v[100],i,j,ok,k;

FILE *f=fopen("pairs.in","r");
FILE *g=fopen("pairs.out","w");

fscanf(f,"%d",&n);
for(i=1;i<=n;i++)
fscanf(f,"%d",&v[i]);
k=0;
for(i=1;i<=n-1;i++)
    if(v[i]==2) {for(j=i+1;j<=n;j++)
		 if(v[j]%2!=0) k++;}
    else {for(j=i+1;j<=n;j++)
	  if(v[j]%2==0) ok=0;
	  for(k=3;(k<=sqrt(v[j])&&(ok==1);k+=2)
	   if(v[j]%k==0) ok=0;

	   if (ok=0) k++;}
	   }
    
fprintf(g,"%d/n",k);

fclose(f);
fclose(g);
return 0;
}