include

int main() { int cont, contAux; double ni, ci; double ira = 0, aux; scanf("%d", &cont); contAux = cont; while(cont) {

    scanf("%lf", &ci);
    if(ci == EOF)break;
    scanf("%lf", &ni);
    if(ni == EOF)break;
    aux = (ci * ni) / (ni * 100);
    ira += aux;
    cont--;
}
ira = ira / contAux;
printf("%.4lf\n", ira);

return 0;

}