#include<cstdio>

FILE *fin=fopen("ciur.in","r");
FILE *fout=fopen("ciur.out","w");

bool a[20000001];
int i,j,k,n;

int main(){
	
	fscanf(fin,"%d",&n);
	
	for(i=2;i<=n;i++)
		a[i]=1;
	
	for(i=2;i<=n;i++)
		if(a[i]){
			for(j=i*i;j<=n;j+=i)
				a[j]=0;
			k++;
		}
	
	fprintf(fout,"%d",k);
	
	return 0;
	
}