#include <cstdio>
#include <cmath>
#include <fstream>
using namespace std;
FILE *f=fopen("ciur.in","r");
FILE *g=fopen("ciur.out","w");
int8_t v[2000001];
int nr;
int main()
{int i,j,st,n;
fscanf(f,"%d",&n);st=sqrt(double(n));
v[2]=1;
for (i=3;i<=n;i+=2) v[i]=1;
for (i=3;i<=st;i+=2) if (v[i]==1) for (j=i*i;j<=n;j+=i) v[j]=0;
for (i=1;i<=n;i++) if (v[i]==1) nr++;
fprintf(g,"%d\n",nr);
return 0;
}