#include<stdio.h>
int main()
{ int i,b,d,k,n;
 char a[200000];
FILE *f,*g;
f=fopen("ciur.in","r");
g=fopen("ciur.out","w");
fscanf(f,"%d", &n);
for(i=2;i<=n;i++){
a[i]=1;
for(d=2;d*d<=n;d+=2)
b=d;
for(;b<=n;b+=2)
a[b]=0;
}
for(i=2;i<=n;i++)
if(a[i])
k++;
fprintf(g,"%d",k);
fclose(f);
fclose(g);
return 0;
}