#include <iostream>
#include <cstdio>
FILE *fin=fopen("ciur.in", "r"), *fout=fopen("ciur.out", "w");
using namespace std;
int n, nr, i, j;
bool c[2000000];
int main()
{
    fscanf(fin, "%d", &n);
    for(i=2;i<=n;i++)
        if(!c[i])
        {
            c[i]=1;
            nr++;
            for(j=i;j<=n;j+=i)
                c[j]=1;
        }
    fprintf(fout, "%d\n", nr);
    return 0;
}