#include <fstream.h>   
int N, cnt;   
char prim[2000005];   
int main()   
{   
    int i, j;   
    ifstream F("ciur.in");   
    ofstream g("ciur.out");   
    F>>N;   
    for (i = 2; i <= N;i++)   
        prim[i] = 1;   
    for (i = 2; i <= N; i++)   
        if (prim[i])   
        {   
           cnt++;   
            for (j = i+i; j <= N; j += i)   
                prim[j] = 0;   
        }   
   g<<cnt;   
    return 0;   
}