#include <stdio.h>
#include <stdlib.h>
#define File_in "ciur.in"
#define File_out "ciur.out"
#define Max 2000000
int A[Max];
int main()
{
    freopen(File_in, "r", stdin);
    freopen(File_out, "w", stdout);
    int n,i,j,nr=0;
    scanf("%d",&n);

    for(i = 1; i <= n; i++)
        A[i] = 1;
    for ( i = 2; i*i <= n; i++){
        if( A[i] == 1)
            for(j = 2 * i; j <= n; j = j + i)
                A[j] = 0;
    }
    for( i = 2; i<= n; i++)
        if(A[i]==1)
            nr++;
    printf("%d",nr);
    return 0;
}