#include<stdio.h>

int n,x,i,j;
char v[2000001];

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