#include <stdio.h>
#include <stdlib.h>   

int main(void)  
{  
int i, j;  
int n, cnt=0, *prim;  
FILE *in,*out;      
in=fopen("ciur.in","r");  
out=fopen("ciur.out","w");  
   
fscanf(in,"%d",&n);
prim=(int*)malloc(n*sizeof(int));  
for (i=2;i<=n;++i)  
	prim[i]=1;  
for (i=2;i<=n;++i)  
	if (prim[i])  
        {  
        	++cnt;  
             	for (j=2*i;j<=n;j+=i)  
                 	prim[j]=0;  
        }  
fprintf(out,"%d\n",cnt);
fclose(in);
fclose(out);  
return 0;  
}