#include <stdio.h>

int n,nr;
int prim[2000005];

int main(void)
{
    int i,j;
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    scanf("%d", &n);
    for (i=2;i<=n;++i)
        prim[i]=1;
    for (i=2;i<=n;++i)
        if(prim[i])
        {
            ++nr;
            for (j=i+i;j<=n;j+=i)
                prim[j]=0;
        }
    printf("%d\n", nr);

    return 0;
}