#include <stdio.h>
FILE*f=fopen("ciur.in","r");
FILE*g=fopen("ciur.out","w");
int n,i,j,v[2000002],x;
char w[2000002];
int main() {
	fscanf(f,"%d",&n);
	for(i=2;i<=n;i++){
		if(w[i]==0){
			x++;
			for(j=i;j<=n;j+=i)
				w[j]=1;
		}
	}
	fprintf(g,"%d",x);
	
	
	fclose(g);
	fclose(f);
	return 0;
}