#include <iostream>
#include <cstdio>
#define N 2000001

using namespace std;

int x, nr, nprim[N];

int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);

    scanf("%d ", &x);
    for(int i=4;i*i<=x;i+=2)
        nprim[i]=1;
    for(int i=3;i<=x;i+=2)
    {
        if(!nprim[i])
            nr++;
        for(int j=2*i;j<=x;j+=i)
            nprim[j]=1;
    }
    if(x>=2)
        nr++;
    printf("%d", nr);
    return 0;
}