#include <stdio.h>
#include <string.h>
int main(void){
    int n,a,b;
    char x[1000000];
    while(~scanf("%d",&n)){
        memset(x,0,sizeof(x));
        for(a=2;a<=n/2;a++)for(b=a*2;b<=n;b+=a)x[b]=1;
        for(a=2,b=0;a<=n;a++)if(!x[a])b++;
        printf("%d\n",b);
    }
    return 0;
}