#include <iostream>
#include <cstdio>
using namespace std;
char ciur[2000001];
int main()
{   int n,i,nr=0;
    FILE *f = fopen("ciur.in","r");
    FILE *g = fopen("ciur.out","w");
    fscanf(f,"%d",&n);
   for(i=2;i<=n;i++)
   {
       if(!ciur[i])
    {
        nr++;
        int j=i;
      while(j<=n)
      { j=j+i;
        ciur[j]=1;
      }

    }
   }
   fprintf(g,"%d",nr);
    return 0;
}