#include<cstdio>
long long i,n,nr;
int main()
{
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
    scanf("%d",&n);
    n=n;
    for(i=10;i<=1000000000;i=i*10)
    {
        if(n<i) break;
    }
    i=i/10;
    while(i>0)
    {
        i=i/10;
        nr++;
    }
    n=(n-nr+1)*5;
    if(n==0) n++;
    printf("%d",n);
    return 0;
}