#include <iostream>
using namespace std;


int main() {

	int judge[1000000];
	for(int k=0;k<1000000;k++)judge[k]=1;
	int n;
	
	while(cin>>n){
		int 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;
}