#include <stdio.h>

using namespace std;
FILE *f=fopen("ciur.in","r");
FILE *g=fopen("ciur.out","w");

int n;
bool cr[2000005];
// p[i]==0 => 2*i+1 e prim
int ciur(int n)
{int i,nr=1,j;

 /* for(i=2;i<=n;i+=1)
 cr[i]=1;*/

for(i=1;((i*i)<<1)+(i<<1)<=n;i+=1)
if (cr[i]==0)
{
 for(j=((i*i)<<1)+(i<<1);(j<<1)+1<=n;j+=(i<<1)+1)
 cr[j]=1;
}
for (i=1;2*i+1<=n;i++)if (cr[i]==0) nr++;
return nr;
}

int main()
{
fscanf(f,"%d",&n);
fprintf(g,"%d",ciur(n));
return 0;
}