#include <bits/stdc++.h>

using namespace std;
int n,i,j,x,cnt;
fstream f ("ciur.in");
ofstream g ("ciur.out");
int main() {

f >> n;
bool nr[n]= {false};
for(i = 2;i<=sqrt(n);i++) {
    if (!nr[i]) {
        for (j = i*i; j<=n;j+=i) {
            nr[j] = 1;
        }
    }
}

for (x = 1;x<=n;x++) {
    if (nr[x] == 0) {
        cnt++;

    }

}
g << cnt - 1;
}