#include <stdio.h>

using namespace std;

const int MAX = 2000000;


bool ciur[MAX + 1];

int main()
{
    FILE *fin, *fout;

    fin = fopen("ciur.in", "r");
    fout = fopen("ciur.out", "w");

    int n;

    fscanf(fin, "%d", &n);

    ciur[1] = 1;
    int cnt = 0;


    for(long long i = 2; i <= n; i++)
    {
        if(ciur[i] == 0)
        {
            cnt++;
            for(long long j = i * i; j <= n; j+=i)
                ciur[j] = 1;
        }
    }

    fprintf(fout, "%d", cnt);

    return 0;
}