#include <cstdio>
#define nMax 2000000

using namespace std;

int i, j, n, nr, v[nMax+5];

void ciur()
{
    v[0]=v[1]=1;
    for(i=4; i<=nMax; i+=2)
        v[i]=1;
    for(i=3; i*i<=nMax; i+=2)
        if(!v[i])
            for(j=i*i; j<=nMax; j+=2*i)
                v[j]=1;
}

int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    ciur();
    scanf("%d", &n);
    for(i=2; i<=n; i++)
        if(!v[i])
            nr++;
    printf("%d", nr);
    fclose(stdin);
    fclose(stdout);
    return 0;
}