#include<bits/stdc++.h>
using namespace std;
int main(){
    bool p[1000000];int n,i,j;
    fill(p,p+1000000,1);p[0] = p[1] = 0;
    for(i=2;i<=999;i++){
        if(!p[i]) continue;
        for(j=i+i;j<1000000;j+=i) p[j] = 0;
    }
    while(cin >> n) cout << accumulate(p,p+n+1,0) << "\n";
}
