#include <stdio.h>
int v[2000008];
int main(){
FILE *in,*out;
in=fopen("ciur.in","r");
out=fopen("ciur.out","w");
int n;


fscanf(in,"%d",&n);
int i,j;
for(i=2;i<=n;i++) {
    for(j=i+i;j<=n;j+=i) v[j]=1;


}
int prime=0;
for(i=2;i<=n;i++)  if(!v[i]) prime++;
fprintf(out,"%d",prime);
fclose(in);
fclose(out);
}