#include <stdio.h>

using namespace std;
const int N = 2000005;
int ciur[N];
int main()
{
    // verificata.
    FILE *in, *out;
    in = fopen ("ciur.in", "r");
    out = fopen ("ciur.out", "w");
    int N,i,j,nr = 0;
    fscanf(in, "%d", &N);
    for (i=2; i <= N; i++)
        if(ciur[i] == 0)
        {
            for(j = i+i; j <= N; j+=i)
                ciur[j] = 1;
            nr++;
        }
    fprintf(out , "%d", nr);
    return 0;
}