#include <cstdio>
#define L 2000001
using namespace std;
bool ciur[L];
int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    int i, j, x, nr=0;
    scanf("%d", &x);
    for(i=3; i<=x; i+=2)
        if(!ciur[i])
        {
            nr++;
            for(j=i*i; j<=x; j+=(i<<1))
                ciur[j]=1;
        }
    printf("%d\n", nr);
    fclose(stdin);
    fclose(stdout);
    return 0;
}