#include <cstdio>

using namespace std;

const int MAX_N = 2000000;

FILE *in, *out;

bool ciur[MAX_N+1];

int main()
{
    in = fopen("ciur.in", "r");
    out = fopen("ciur.out", "w");
    int n;
    int nr = 0;
    fscanf(in, "%d", &n);
    for(int i = 2; i <= n; i++)
    {
        if(!ciur[i])
        {
            nr++;
            for(int j = i*i; j <= n; j += i)
                ciur[j] = true;
        }
    }
    fprintf(out, "%d", nr);
    fclose(in);
    fclose(out);
    return 0;
}