#include <stdio.h>

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

int n;
bool cr[2000005];

int ciur(int n)
{int i,nr=1,j;

 for(i=2;i<=n;i+=2)
 cr[i]=1;
for(i=3;i<=n;i+=2)
if (cr[i]==0)
{
  nr++;
 for(j=i*i;j<=n;j+=i)
 cr[j]=1;
}

return nr;
}

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