#include<stdio.h>
FILE*f = fopen("ciur.in","r");
FILE*g = fopen("ciur.out","w");

char v[20000005];
int i,n,j,nr;
int main () {
	fscanf(f,"%d",&n);
	for(i=2;i<=n;i++){
		if(v[i]==0){
			nr++;
		}
			for(j=i+i;j<=n;j+=i)
				v[j]=1;
	}

	fprintf(g,"%d",nr);
	
	
	fclose(f);
	fclose(g);
	return 0;
}