#include<iostream>

using namespace std;
int prime[1000000];

int main(){
	
    prime[0]=-1;
    prime[1]=-1;
    
    for(int i=2;i<1000000;i++){ 
    
        if( prime[i] == 0 ){
        	
            prime[i] = 1;
            for(int j=i*2;j<1000000;j+=i)
			prime[j] = -1 ;
			
        }
        
    }
    int a;
    while( cin >> a ){
    	
        int count = 0;
        
        for(int i=1;i<a+1;i++)
		if(prime[i] == 1)
		count++;
		
        cout << count << "\n";
    }
    return 0;
}
