#include <fstream>
using namespace std;
int main (){
	long long n,i,j,m=0;
    char prim[2000005];
	
	
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    
    fin>>n;
    for (i=2;i<=n;i++){
        prim[i]=1;
	}
    for (i=2;i<=n;i++){
        if (prim[i]==1){
            m++;
            for (j=i*i;j<=n;j=j+i){
                prim[j]=0;
			}
        }
	}
    fout<<m;
    return 0;
}