#include <bits/stdc++.h>
#define SIZE 2000001
/// TONI BO$$ was here
/// #MLC

using namespace std;

char ciur[SIZE];

int main()
{
    int i,j,n,nr;
    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*i; j<=n; j+=i)
                ciur[j]=1;
    nr=0;
    for(i=2; i<=n; i++)
        nr+=(ciur[i]==0);
    printf("%d",nr);

    return 0;
}