#include <stdio.h>
#include <vector>
#define size 2000001

using namespace std;
vector<bool> ciur(size,true);

int main()
{
    int n,i,j,s = 0;
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    for(i = 2; i*i < n; i++)
        if(ciur[i])
            for(j = i; j*i <n; j++)
                ciur[j * i] = false;
    for(i = 2; i < n; i++)
        if(ciur[i])
            s++;
    printf("%d",s);

    return 0;
}