#include <iostream>
#include <cstdio>
using namespace std;
FILE *fin=fopen("ciur.in", "r");
FILE *fout=fopen("ciur.out", "w");
bool ciur[2000005];
void eratostene()
{
    ciur[0]=ciur[1]=1;
    for (int i=2; i*i<=2000000; i++) {
        if (ciur[i]==0) {
            for (int j=i*i; j<=2000000; j+=i) {
                ciur[j]=1;
            }
        }
    }
}
int main()
{
    eratostene();
    int n;
    fscanf(fin, "%d", &n);
    int cnt=0;
    for (int i=2; i<=n; i++) {
        //cout<<i<<" "<<ciur[i]<<endl;
        if (ciur[i]==0) cnt++;
    }
    fprintf(fout, "%d", cnt);
    return 0;
}