#include <stdio.h>

int main()
{
    int x, i, c;
    scanf("%d", &x);

    x = x - 2;
    c = 2;

    for(i=1; i<=x; i++){
        c = c+2;
    }
    c = c + 1;
    printf("%d\n", c);

    return 0;

}