#include <stdio.h>

int main()
{
    FILE *f,*g;
    f = fopen("fact.in","r");
    g = fopen("fact.out","w");
    long int n,j,k;
    fscanf(f,"%ld",n);
    j = 5*n;
    k = n/2;
    j = j + k;  
    fprintf(g,"%ld",j);
    fclose(f);
    fclose(g);
    return 0;
}