#include <iostream>
using namespace std;


int main() {

	int judge[1000000];
	for(int k=0;k<1000000;k++)judge[k]=1;
	int n,sum;
	
	while(cin>>n){
		if(n==0||n==1){
			sum = 0;
		}else{
			sum = 1;
			for(int i=3;i<n+1;i+=2){
				if (judge[i]==1){
					sum++;
					for(int j=2;j<=n/i;j++)
						judge[i*j] = 0;
				}	
			}
		}
		
		cout << sum <<endl;
	}

	return 0;
}