#include <stdio.h>
char v[2000000];
int main()
{int n,nr=0,i,j;
FILE *fin,*fout;  
fin=fopen("ciur.in","r");
fout=fopen("ciur.out","w");
fscanf(fin,"%d",&n);
for (i=2;i<=n;++i)
if(v[i]==0)
{++nr;
for(j=i+i;j<=n;j+= i)
v[j]=1;
}
fprintf(fout,"%d",nr);
return 0;
}