#include <stdio.h>

int main()
{
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
    long long int p, n, i, j, c;
    scanf("%lld",&p);
    if (!p) printf("1\n");
    else for ( i = 4*p; i <= n; i++ )
    {
        j = 0;         
        //if ( i / 5 > p ){ printf("-1\n"); break; }
        c = i;
        while(c > 5)
        {
                j += c / 5;
                c = c / 5;
        }
        if ( j == p ) { printf("%lld\n",i+1); break; }        
    }
    return 0;
}