#include <stdio.h>
#include <stdlib.h>
int main () {
FILE *fin, *fout;
int n, cnt=0, i, prim[20000005],j;
fin=fopen("ciur.in","r");
fout=fopen("ciur.out","w");
fscanf (fin, "%d", &n);

prim[0]=prim[1]=0;
for (i=2; i<=n; ++i) 
prim[i]=1; //pp ca toate sunt prime, folosind un vector de frecventa

for (i=2; i<=n; ++i)
 if (prim[i]) {
cnt++; 
for(j=i+i; j<=n; j+=i) prim[j]=0;
}
fprintf (fout, "%d", cnt);
fclose(fin); fclose (fout);
return 0;
}