#include <bits/stdc++.h>

using namespace std;
const int N=2000005;
bitset <N> b;
int v[N];

int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);

    int n,i,j,nr=0;
    scanf("%d",&n);
    for(i=2;i*i<=n;i++){
        if(!b[i]){
            for(j=i*i;j<=n;j+=i) b[j]=1;
        }
    }
    for(i=2;i<=n;i++){
        if(!b[i]) nr++;
    }
    printf("%d\n",nr);

    return 0;
}