#include<iostream>
#include<cstring>

int PrimeCount(int n){
	int A[n+5];
	memset(A,0,sizeof(A));//0は素数
	for(int i=2;i*i<=n;i++){
		if(A[i]==0){
			for(int j=i*2;j<=n;j+=i){
				A[j]=1;
			}
		}
	}
	int count=0;
	for(int i=2;i<=n;i++){
		if(A[i]==0) count++;
	}
	return count;
}

int main(void){
	int n;
	while(std::cin>>n){
		std::cout<<PrimeCount(n)<<std::endl;
	}
	return 0;
}

