#include <cstdio>

using namespace std;

int main()
{
    int p;
    FILE *f = fopen("fact.in","r");
    FILE *g = fopen("fact.out","w");
    fscanf(f,"%i",&p);
    if(p != 0)
    {
        int k = p*5,x = 1;
        while((double)k/(5*5*x) > 1)
            x ++;
        x --;
        fprintf(g,"%i",(p - x)*5);
    }
    else
        fprintf(g,"1");
    return 0;
}