#include <bits/stdc++.h>

using namespace std;

char vaz[2000010];

int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    int n,sol=0;
    scanf("%d",&n);
    for(int i=2;i<=n;i++)
        if(!vaz[i])
        {
            sol++;
            for(long long j=1LL*i*i;j<=n;j+=i) vaz[j]=1;
        }
    printf("%d",sol);
    return 0;
}