#include<fstream>
using namespace std;
int n,k,i,j;
bool c[2000001];
void inc(){
for(i=2;i<=n;++i){
    c[i]=1;
}
}
void rez(){
 for(i=2;i<n+1;++i){
    if(c[i]==1){
        k++;
        for(j=i+i;j<n+1;j+=i){c[j]=0;}
    }
 }
}

int main(){
 FILE *f1, *f2;
 f1=fopen("ciur.in","r");
 f2=fopen("ciur.out","w");
 fscanf(f1,"%d",&n);
 inc();
 rez();
 fprintf(f2,"%d \n", k);

fclose(f1);
fclose(f2);
}