#include <stdio.h>

FILE*f=fopen("ciur.in","r");
FILE*g=fopen("ciur.out","w");
int n,i,j,nrprime;
char sir[2000002];

int main () {
	
	fscanf(f,"%d",&n);
	
	for(i=2;i<=n;i++){
		if (!sir[i]){
			nrprime++;
			for (j=i+i;j<=n;j+=i){
				sir[j]=1;
			}
		}
	}	
	
	fprintf(g,"%d",nrprime);
	
	fclose(f);
	fclose(g);
	return 0;
	
}