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